O you who believe! When you incur debt among yourselves for a certain period of time, write it down. And have a scribe write in your presence, in all fairness. And let no scribe refuse to write, as God has taught him. So let him write, and let the debtor dictate. And let him fear God, his Lord, and diminish nothing from it. But if the debtor is mentally deficient, or weak, or unable to dictate, then let his guardian dictate with honesty. And call to witness two men from among you. If two men are not available, then one man and two women whose testimony is acceptable to all—if one of them fails to remember, the other would remind her. Witnesses must not refuse when called upon. And do not think it too trivial to write down, whether small or large, including the time of repayment. That is more equitable with God, and stronger as evidence, and more likely to prevent doubt—except in the case of a spot transaction between you—then there is no blame on you if you do not write it down. And let there be witnesses whenever you conclude a contract, and let no harm be done to either scribe or witness. If you do that, it is corruption on your part. And fear God. God teaches you. God is aware of everything.

The Holy Quran · Al-Baqara (The Cow) · 2:282