MOBILE
BANK IN THE PERSPECTIVE OF THE ISLAMIC ECONOMY
Aang Gunaepi1, Ryan
Bianda2, Muhammad Misbakul Munir3
Sekolah
Tinggi Ilmu Syariah Al Wafa, Bogor, Indonesia
�[email protected]1, [email protected]2, [email protected]3
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ABSTRACT
Mobile banking is a widespread practice in many
areas throughout Indonesia. There are many
reasons for this, both internal and external. This study aims to find out and
analyze the definition, history, and practice of mobile banking, then review it
from the perspective of Islamic Economics. This study uses a qualitative method
by reviewing related literature on mobile banking and its practices in various
regions in Indonesia. In the Islamic economy, financial inclusion is very
important because the financial system is geared to promote people's welfare.
The practice of debts through mobile banks can be carried out with several
principles that must be obeyed, including murabahah, mudharabah, and
musyarakah. During obligations through portable banks, mobile banks must ensure
that all transactions follow sharia principles. The Islamic solution to
preventing the practice of mobile banking is to carry out financial planning
through a priority scale of needs, educate the public about the Islamic economy
through Islamic financial institutions, and maximize the role of zakat for
mustahik.
Keywords: mobile
banking, islamic economics, islamic sharia.
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Corresponding Author: Aang
Gunaepi
E-mail: [email protected]
INTRODUCTION
Following the
mandate of the law article 33 paragraph 1, the economy adopted in Indonesia has
a family principle so that in practice, it must consider the balance of each
element of development so that economic growth and national stability lead to
the same goal, namely increasing the standard of living of humans as much as
possible (Hastuti, 2016).
In addition, the economy must
ensure justice for the people of Indonesia. So that the government issues
regulations on banks so that their business can be carried out on the principle
of economic democracy following its main function, accepting deposits and
distributing credit to create new purchasing power and circulate and traffic
money from the public (Sunardi, 2021).
In
principle, economic values should not be separated from ethics and morals. Many
people have begun to realize this, so much effort has been made to find an
ideal economic model. Due to the current facts, economic growth is not
accompanied by equal distribution of income and welfare for the general public.
Coupled with an increase in population which makes the space for competition
even greater, which requires a humane economic order to realize justice (Yusuf & Al Arif,
2015).
To bridge
the surplus units and deficit units, financial institutions are presented as
intermediary institutions so that people can move the wheels of the economy by
investing or increasing the ratio of productive business capital or consumptive
meeting needs according to the needs of each party, as God has outlined (Tama, 2015). Surplus units destined for good fortune; deficit units provided.
These differences aim to help each other, synergize, and collaborate in
goodness.
As a Muslim, of course, he
believes that everything must follow Islamic rules and regulations. From an
Islamic perspective, economics is certainly the essence of Islamic teachings
related to life problems as a solution to social and economic issues (Society., 2018). Among the highlights of the Islamic economy is usury,
which still occurs a lot in society.
Among the practices of usury that
are rife and even more widespread in society is mobile banking, a debt practice
under the name of a cooperative or finance. The portable bank was born
from the segmentation of financial institutions, which in its development was a
response to the regulations that apply to formal institutions. Customers of
this mobile bank are also inseparable from members of the community consisting
of traders, homemakers, and other people, most of which consist of the
economically vulnerable group. With a family approach and convenience not found
in banking financial institutions, mobile banks have a special attraction for
people in various regions of Indonesia.
Several studies state that the
practice of mobile banking occurs in many regions in Indonesia. The research
was conducted to analyze and overcome this phenomenon. Among them is Sutrisno
Badri's investigation, which concluded that mobile bank operations impacted
decreasing debtors in the tambay at batik entrepreneur cooperative in Klaten (Badri, 2012). Sakinah's research concluded that the community in Sejati
Village, Camplong, Kab. Sampang prefers to borrow
from mobile banks rather than make Qardul Hasan transactions at Islamic banks (Sakinah, 2016). Syafira Putri Pertiwi's research concluded that mobile banking
is quite disturbing in Leuwisadeng Village, Bogor,
so it is necessary to conduct training for homemakers to be free from bank
shackles. Mobile research by Lisa Dewi Anggraeni concluded that the practice of
mobile banking in the Cilalawi area of Purwakarta is
increasing because public interest is also growing due to several factors (Pertiwi, 2018). The biggest one is due to the convenience factor and the ability
to solve financial problems quickly (Dewi Anggraeni, 2020).
The place of research, when viewed
from the point of view of the religion adhered to, is a population with a
Muslim majority. In fact, in several research locations, 95% of the population
is Muslim, namely Bogor, Sampang, and Purwakarta (bps.go.id, 2019). This research is interesting because one of the practices
commonly occurs among a majority. The Muslim population is a practice that
includes things prohibited by religion. For this reason, the author must review
this phenomenon from an Islamic economic perspective so that it can add insight
and scientific treasures for the community so that they can avoid usury
practices caused by transactions with mobile banks. This research aims to find
out and analyze portable banks from the perspective of Islamic economics. The
benefits of this research are to provide a better understanding of portable
banks as a financial product, contribute to the development of the Islamic
financial industry, increase public awareness and understanding of Islamic
finance and Provide policy recommendations to the government.
METHODS
This study uses a
qualitative method by reviewing related literature on mobile banking and its
practices in various regions in Indonesia, reviewing previous research to draw
conclusions then and provide new insights from an Islamic economic perspective.
RESULTS
AND DISCUSSION
In language, a bank is a financial institution or
institution that has the main function of intermediary between surplus and
deficit units in society and provides credit and services in payment traffic
and money circulation (Uang, 2017). The word circumference means around or the environment
around something. Meanwhile, mobile banks are etymologically individual
institutions that charge high-interest rates when providing daily loans and
billing. It is called traveling because billers travel from one place to
another in billing. In the next stage, many lending and borrowing activities are
illegal or unofficial, with high-interest rates.
In a developing country like Indonesia, mobile banking
has been introduced previously. Born and developed due to the segmentation of
financial institutions that are not managed by the state or market and are not
under the protection, supervision, and regulation of national and international
central banks. Institutionally, the majority of mobile banks are informal
financial institutions. One of the characteristics of informal financial
institutions is that their role starts as a community to help themselves and
develop into brokerage institutions per the path of community economic
development, which is then used as a solution to life's difficulties in crises
(Soemitra, 2018). Its customers tend to come from the lower middle class,
and the trust factor is sufficient; it does not require many administrative
requirements as loan
guarantees. This convenience is why mobile banks are increasingly in
demand by the public. Simple administration and easy contracts seem to be a
breath of fresh air from your current difficulties.
In several regions in Indonesia, this mobile
banking practice is rife with various names. In West Java, this practice is
better known as Emok Bank. In Central Java, it is better known as title or bank
plecit. Mobile banks operating mostly in the community often need a legal
entity. Usually, individuals or groups who have excess money open this business
by distributing loans to those in need.
Externally, the factors that trigger people
to use mobile bank services include:
Cultural
factors
Culture is a habit that is deeply rooted and
difficult to change, consisting of basic values, opinions, or views on
something. Each community group must have a culture that develops and becomes
an unwritten rule that is the hallmark of that society. Usually determined by
religion, racial group, geographic region, and social class. Usually, within
one community, people have relatively the same economic type and income
sources, with the same financial problems (Anggraeni et al., 2020).
Social factors
In social life, every social entity influences one another. Where other
individuals simultaneously influence one individual influences and. Affecting
individuals are included in the primary group category of the closest
environment, such as family, friends, and neighbors.
Personal
factor
This factor is the dominant thing affecting an individual. The age range
usually determines a person's personality because changes in consumption
patterns tend to change at a certain age range or because of work, economic
situation, and lifestyle (Anggraeni, 2020).
Psychological
factors
Psychological factors include motivation, learning,
perception, personality, and attitude. In addition to the factors above, the
main factor that causes a family to interact with a mobile bank is the weak
economic condition, which is unable to meet daily basic needs. Regarding basic
meeting needs, while conditions are not possible, some families apply a
strategy that, according to Suharto, is called a coping strategy.
In language, strategic
coping is a strategy for overcoming a problem or problem (Maryam, 2017). The definition in general can be
interpreted as a set of ways a person applies to overcome the issues that occur
in his life through certain mechanisms to achieve better conditions. But, it
can be interpreted that strategic coping is a survival strategy for overcoming
economic problems. These
strategies include the following:
1.
Active
strategy, namely optimizing all resources and potential. Such as taking
overtime for employees or wild plants and used goods that are recycled.
2.
Passive
strategy, namely completing expenses with income. Expenditures related to
consumption, education, and so on are adjusted to the income earned.
3.
Network
strategy, namely utilizing the surrounding social networks, such as making
loans to local neighbors, close family, or mobile banks
These three strategies are
household solutions that are widely used in overcoming income problems. And that is part of the family's positive
response to dealing with issues. The choice of such a strategy depends on the
most effective possibility of solving the problem. And the most crucial problem is the most urgent need because humans have levels of conditions
that are top priority to be fulfilled sequentially (Order, 2016).
These human needs are classified into the following five levels:
1.
Physical
conditions, namely biological needs, and survival
2.
The need for
security, safety, and freedom from fear and threats
3.
Social needs,
such as belonging, acceptance, and affection
4.
The need for
appreciation of status, position, achievement
5.
The need for
self-actualization, self-development, and following the desired passion
Of the five levels of human needs, physical needs are the top
priority to be fulfilled and are urgent. For this reason, if the active and
passive strategies can no longer solve the problem, the solution is to carry
out a network strategy and make loans to neighbors, relatives, and mobile
banks.
The characteristics of mobile banks are as follows:
1.
Has no formal
office and usually travels from one group to another
2.
It does not
require difficult administrative requirements to get a loan
3.
Give loans at
high-interest rates with easy loan guarantees
4.
Its customers
tend to be from the lower middle class.
In some cases, mobile banks are considered better than large banks
or other formal financial institutions for several reasons;
1.
Ease of
making loans with simple conditions. Usually, with a photocopy of the KTP,
prospective customers can get a loan quickly.
2.
The loan
amount does not have to be large. Mobile banks even provide loans of hundreds
of thousands of rupiah.
3.
Mobile banks
are more proactive in picking up the ball by visiting their prospective
customers regularly.
These conveniences cause problems because it deals with mobile
banks. Starting from cases of being in debt with a large amount, acts of
violence, and even the loss of life.
At least there are two negative impacts of interacting with mobile
banks (Feny Mukhtaliana, 2020):
1.
Tendency to
behave consumptively
There is a saying that if someone already has one mountain of
gold, he will try to get a second, third, and so on. It shows that humans tend
to be dissatisfied with fulfilling lust even though it is excessive. The only barrier to desire is the human
conscience itself. Likewise, when people are used to looking for shortcuts to
meet their needs through mobile banks, it will be easier to control when other,
bigger problems arise.
2.
Household
economic resilience becomes vulnerable
Difficulties in life are undeniable. It is like a necessity when
life is lived even though everyone has problems. Likewise, when there is an
urgent need, and you start interacting with mobile banks, your life order
changes because you must start thinking about finding and setting aside income
to pay off loans every day.
Mobile Banks in the Perspective of Islamic Economics
As social
beings, humans can never meet all their needs alone. He needs to interact and
be in a community to help each other. God created humans in various forms, to various
advantages, so they work together. Word of Allah swt:
وَاللّٰهُ
فَضَّلَ
بَعْضَكُمْ
عَلٰى بَعْضٍ
فِى
الرِّزْقِۚ�
�Allah has excelled some of you
over others in terms of sustenance.�
(QS An-Nahl: 71)
Everyone has their way of meeting
their needs. As a Muslim, the business is carried out according to the
teachings of the Koran and hadith. One of the teachings contained in the Koran
is about accounts payable.
In fiqh literacy, debt is called
al -card with the pillars and conditions determined by both the debtor
and the debtor. In simple terms, we often know it by other terms such as
credit. The word honor comes from credo which means to lend with the principle
of trust (Karim, 2001).
Credit practices and accounts
payable that apply to mobile banks are loans with high interest. From an
Islamic perspective, this practice is a prohibited ribawi transaction because
it takes benefits or profits from a loan. In this case, the following fiqh rules
apply (Sahroni, 2018):
كُلُّ
قَرْضٍ جَرَّ
نَفْعًا
فَهُوَ رِبا
"Every debt that brings benefits (to the person who owes it)
then is usury".
Riba, in the case of debts, is
included in the usury fadl, the condition for exaggerating the loaned
property when it is returned by the debtor (Antonio, 2001).
the situation is exacerbated by
the fact that these benefits are taken from poor people who should get help
because they tend to be in debt for consumptive things (Oktaviani. J, 2018). The practice of usury, which superficially can grow the economy,
does the opposite because it undermines socio-religious values and norms.
Because of urgency, people who are
entangled in debt with mobile banks should get help. Helping each other in
goodness is a noble Islamic teaching, as the word of Allah swt
وَتَعَاوَنُوْا
عَلَى
الْبِرِّ
وَالتَّقْوٰىۖ
وَلَا
تَعَاوَنُوْا
عَلَى
الْاِثْمِ
وَالْعُدْوَانِ
ۖ
�"Please help
you in (doing) virtue and piety, and do not help each other in sin and
enmity." (QS Al-Maidah: 2)
Among the forms of helping each
other in kindness is lending to those in need. Al-Quran mentions that people
who give loans have priority and glory with Allah SWT. In His words,"
whoever owes a debt because of Allah with a good debt, Allah will multiply the
return of the loan for him, and he will get a lot of rewards" (Al-Hadid:
11).
Islamic Solutions for Mobile Banks
Studies on holistic economics are indeed being carried out because
the source comes from religious values that align with human life's long-term
goals.
Islamic economics, as a guide full of religious values in
muamalah, provides practical solutions to overcome social phenomena in society
in economic terms. One is a debt-receivable activity through mobile banks,
which hurts family social order.
Do Financial Planning
Islam views every activity must be planned as well as possible. So
that it does not just follow the currents and gusts of wind that blow it in any
direction but follows the roadmap that has been planned. For that, Allah swt.
Said:
يَا
أَيُّهَا
الَّذِيْنَ
آمَنُوْا
اتَّقُوْا
اللهَ وَلْتَنْظُرْ
نَفْسٌ
مَاقَدَّمَتْ
لِغَدٍ
�O you who believe! Fear Allah and
let everyone pay attention to what he has done for tomorrow" (QS Al-Hashr:
18)
This verse implicitly teaches that
everything you want to do should be planned well in advance to get a priority
scale of the good things that will be done. About the family from an economic
standpoint, every family should do good financial planning, adjusting their
capabilities.
So, it focuses on needs not wants, trying to meet basic and urgent
basic needs, not on markets that are complementary and tend not to be binding.
Financial planning can start by analyzing current economic conditions,
determining financial goals, making choices to meet needs, implementing planned
financial programs, and ensuring the effectiveness of planning programs that
have been made (Sundjaja, 2010).
Wife Helping Husband Finances.
If the
ability of the head of the household is limited while the basic and urgent
basic needs have not been met, it is not a problem if a wife helps with the
family finances. Even in Islam, the role of women outside the home is not
prohibited as long as their work follows the guidelines and established rules (Sundjaja, 2010).
Among the
criteria for work outside the home that a Muslim woman may do are as follows (Hafil, 2020):
a.
The work that
is done is not in the form of disobedience to Allah SWT and does not tarnish
the honor of the family
b.
It does not
require a Muslim woman to be alone with a man who is not a mahram
c.
Her job does
not require her to wear excessive make-up or make-up or require her to open
her private parts.
d.
Do not do
strenuous or physically risky work
e.
Her work does
not deprive her of the role of a wife at home
The Need for Education and Socialization of Islamic Economics for
Muslims
One of the problems with the widespread practice of mobile banking
is the low level of public knowledge about the concept of debt from an Islamic
perspective, its terms, and its differences from usury. Some community members
carry out this practice out of ignorance. For this reason, the active role of
Islamic financial institutions is urgently needed by providing education and
understanding of Islamic financial products that can be used.
One of the motives for establishing Islamic financial
institutions, be it banking, cooperatives, or BMTs, is to minimize and prevent
transactions prohibited by sharia in society. Of course, part of introducing
Islamic financial products is by going directly to the community, providing
education and knowledge for people who are unfamiliar with Islamic finance. So
that the wider community knows and understands that there is a financial system
that reflects the noble Islamic sharia values and is considered fair and
prosperous (Sholihin, 2015).
By actively providing education to the surrounding community, it
is hoped that it will broaden horizons and increase public knowledge, which in
turn can prevent them from practicing debt through mobile banks.
In addition to the active role of financial institutions, the role
of religious leaders in society also needs to be maximized. Providing sermons,
recitations, and other religious activities with sharia economic content and
Islamic muamalah, which are rarely carried out.
With the synergy of the role of institutions and community
leaders, it is hoped that they will be able to increase public knowledge about
the urgency of conducting transactions following sharia principles following
the religious teachings they believe in, free from mobile bank practices and
migrating to sharia financial institutions.
Maximize the Role of Zakat
One of the social values contained
in Islam is that the difference in each person's ability to obtain wealth is
very conscious. For this reason, so that social inequality and jealousy do not
occur because of these differences, Islam requires people with excess assets to
spend part of their wealth, then allocate it to people lacking and needing it.
That obligation is zakat.
Zajat is not only an obligation,
but it is one of the foundations of Islam, where if it is not fulfilled, one's
Islam will not be perfect, as sad Rasulullah saw.
بني
الإسلام على
خمس : شهادة أن
لا إله إلا
الله ، وأن
محمدا رسول
الله ، وإقام
الصلاة ، وإيتاء
الزكاة ، وحج
البيت ، وصوم
رمضان
) رواه البخاري ومسلم (
One of the
motives for some families to practice debt through a mobile bank is due to the
ease of terms and requests from the portable bank; if they go to a formal
financial institution, they are likely to be rejected because the
administrative requirements are more complicated and cannot be fulfilled, while
the needs that must be met are basic and urgent. Families with conditions like
this should get attention from zakat, where one group of zakat recipients is
poor with one of the characteristics, namely families with income that is not
sufficient for their basic needs (Sahroni, 2018). Meanwhile, families already in debt to mobile banks because they
meet their family's basic needs can be included in the grim category to free
them from the debt bondage of portable banks whose nominal values are getting
bigger and bigger.
In terms of productivity, families who are included in the zakat
recipient group can be empowered so that they experience an increase in their
standard of living through the zakat empowerment program. The model for the
distribution of zakat funds consists of four forms: (Nst, 2021) First is
traditional consumptive, second is creative consumptive, third is traditional
productive, and fourth is creative production. The four distribution models of
zakat funds can be adapted to the zakat recipients' conditions. With the zakat
fund empowerment program, the long-term agenda for mustahik is to turn them
into muzak.
CONCLUSION
The practice of debts or loans through mobile banks is
a practice that occurs a lot in regions in Indonesia. From the perspective of
sharia economics, the method of obligations through portable banks is one usury
transaction because there are additional conditions for the nominal amount of
funds returned. This transaction is included in fadhl riba, namely usury, because of the
addition of debt practices. Islamic solutions to prevent mobile banking
practices include carrying out financial planning through prioritizing needs,
the role of wives in the non-domestic sphere, educating the public about
Islamic economics by Islamic financial institutions and religious leaders, and
maximizing the role of zakat for mustahik.
REFERENCES
Anggraeni, L. D. (2020). Analisis Faktor yang Mempengaruhi
Masyarakat Muslim Menggunakan Jasa �Bank Emok.� EKSISBANK: Ekonomi Syariah
Dan Bisnis Perbankan, 04(2), 24.
Anggraeni, L. D., Cahyo Sucipto, M., & Rohmat, S. (2020).
Analisis Faktor Yang Mempengaruhi Masyarakat Muslim Menggunakan Jasa �Bank
Emok� Di Desa Cilalawi Kecamatan Sukatani Kabupaten Purwakarta. EKSISBANK:
Ekonomi Syariah Dan Bisnis Perbankan, 4(2), 168�187.
https://doi.org/10.37726/ee.v4i2.84
Antonio, M. S. (2001). Bank syariah:
dari teori ke praktik. Gema Insani.
Badri,�
sutrisno al. (2012). Implikasi Operasional Bank Keliling Terhadap
Eksistensi Koperasi Pengusaha Batik Tembayat Kecamatan Bayat-Klaten (Studi
Empirik dalam Mekanisme Penyaluran Kredit). Jurnal Orasi Bisnis, November,
27�36.
Berurutan, K. manusia memiliki tingkatan
kebutuhan (maslow : 1995) yang menjadi prioritas utama untuk dipenuhi
secara. (2016). Manajemen sumberdaya manusia: Aktivitas utama dan
pengembangan SDM. Universitas Brawijaya Press.
bps.go.id. (2019). Jumlah Penduduk
Menurut Kabupaten/Kota dan Agama yang Dianut, 2019.
Https://Bekasikab.Bps.Go.Id/Statictable/2021/06/22/1864/Jumlah-Penduduk-Menurut-Kabupaten-Kota-Dan-Agama-Yang-Dianut-2019.Html.
Dewi Angggraeni, L. (2020). Analisis
Faktor Yang Mempengaruhi Masyarakat Muslim Menggunakan Jasa �Bank Emok� Di Desa
Cilalawi Kecamatan Sukatani Kabupaten Purwakarta. EKSISBANK (Ekonomi Syariah Dan Bisnis Perbankan), 4(2), 168�187. https://doi.org/10.37726/EE.V4I2.84
Feny Mukhtaliana. (2020). analisis permintaan kredit pada
bank keliling dan pengaruhnya terhadap kesejahteraan masyarakat di kabupaten
sidoarjo. Skripsi, Universitas Islam Negeri Sunan Ampel, 87.
Hafil, M. (2020). Pandangan Islam bagi Muslimah yang
Bekerja | Republika Online. Republika.Co.Id.
Hastuti, T. (2016). Pendekatan Interdisipliener Hukum Ekonomi
Dalam Pembangunan Sistem Hukum Ekonomi Nasional. Jurnal Ilmiah Dunia Hukum,
1(1), 73�90.
Karim, A. A. (2001). Ekonomi Islam;
Suatu Kajian Kontemporer. Gema Insani Press.
Maryam, S. (2017). Strategi coping: Teori dan sumberdayanya. Jurnal
Konseling Andi Matappa, 1(2), 101�107.
Masyarakat., E. dalam perspektif islam tentu merupakan
intisari ajaran islam yang berkaitan dengan masalah kehidupan sebagai salah
satu solusi dalam masalah ekonomi sosial di tengah. (2018). Ekonomi Mikro
Islam: Islamic Microeconomics. Unimma Press.
Nst, W. (2021). Sosiologi Pemberdayaan Ekonomi Umat Melalui
Dana Zakat. Jurnal
Sosiologi Dialektika Sosial, 7(1).
Oktaviani.J. (2018). Riba dalam Islam. Riba
Dalam Islam, 51(1), 51.
Pertiwi, S. P. (2018). Pelatihan bagi
ibu rumah tangga sebagai upaya penanggulangan jeratan bank keliling. Jurnal Pendidikan Luar Sekolah, 12(1). https://doi.org/10.32832/jpls.v12i1.2907
Sahroni, O. (2018). Fikih Zakat Kontemporer (1st ed.).
Rajawali Press.
Sakinah, S. (2016). Penerapan Al-Qardl Pada Bank Keliling
(Studi Kasus Di Grugek Desa Sejati Kecamatan Camplong Kabupaten Sampang). NUANSA:
Jurnal Penelitian Ilmu Sosial Dan Keagamaan Islam, 13(1), 1�22. https://doi.org/10.19105/NUANSA.V13I1.875
Sholihin, A. I. (2015). Ini Lho Bank Syariah. PT Gramedia Pustaka Utama.
Soemitra, A. (2018). Peran pemberdayaan masyarakat oleh lembaga keuangan mikro
syariah dalam perspektif sustainable development goals (SDGs).
Sunardi, D. (2021). Hukum Perbankan dan Perbankan Syariah.
Penerbit A-Empat.
Sundjaja, A. M. (2010). Perencanaan Keuangan untuk Mencapai
Tujuan Finansial. ComTech: Computer,
Mathematics and Engineering Applications, 1(1), 183�191. https://doi.org/10.21512/COMTECH.V1I1.2218
Tama, C. M. (2015). Studi Financial Inclusion dan
Financial Deepening di Indonesia.
Uang, B. memiliki arti badan atau lembaga keuangan yang
memiliki fungsi utama sebagai intermediasi antara unit surplus dan devisit di
tengah masyarakat serta memberikan layanan kredit dan jasa dalam lalulintas
pembayaran dan peredaran. (2017). Bank & Lembaga Keuangan Syariah.
Prenada Media.
Yusuf, B., & Al Arif, M. N. R.
(2015). Manajemen sumber daya
manusia di lembaga keuangan syariah. Rajawali Pers.
|
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