You who believe! When you take on a debt for a specified period, write it down. A writer should write it down between you justly. No writer should refuse to write; as Allah has taught him, so he should write. The one incurring the debt should dictate and should have fear of Allah his Lord and not reduce it in any way. If the person incurring the debt is incompetent or weak or unable to dictate, then his guardian should dictate for him justly. Two men among you should act as witnesses. But if there are not two men, then a man and two women with whom you are satisfied as witnesses; then if one of them forgets, the other can remind her. Witnesses should not refuse when they are called upon. Do not think it too trivial to write down, whether small or large, with the date that it falls due. Doing that is more just in Allah’s Sight and more helpful when bearing witness and more likely to eliminate any doubt—unless it is an immediate transaction hand-to-hand, taken and given without delay. There is nothing wrong in your not writing that down. Call witnesses when you trade. Neither writer nor witness should be put under pressure. If you do that, it is deviancy on your part. Have fear of Allah, and Allah will give you knowledge. Allah has knowledge of all things.” (Surat al-Baqara; 282)
In this verse, Allah clearly states that believers must keep records of their debts. Believers cannot disregard this commandment because of kinship, assumed sincerity or friendship. This commandment applies to every-one, no matter how much the debt may be, since there is no exception to this obligation. Therefore, sincere believers should behave according to this command in the Qur’an, without reserve.
Allah makes it clear that such a precaution is the best way to eliminate doubt, misunderstandings or injustice in the future. There is no reason not to comply with this injunction.