In the Name of Allah, the Most Gracious, the Most Merciful
God has provided guidance about all aspects of human life including business interaction. Here is what the Holy Qur'an says about business transactions:
“O believers! When you deal with each other in lending for a fixed period of time, put it in writing. Let a scribe write it down with justice between the parties. The scribe, who is given the gift of literacy by Allah, should not refuse to write; he is under obligation to write. Let him who incurs the liability (debtor) dictate, fearing Allah his Rabb and not diminishing anything from the settlement. If the borrower is mentally unsound or weak or is unable to dictate himself, let the guardian of his interests dictate for him with justice. Let two witnesses from among you bear witness to all such documents, if two men cannot be found, then one man and two women of your choice should bear witness, so that if one of the women forgets anything the other may remind her. The witnesses must not refuse when they are called upon to do so. You must not be averse to writing (your contract) for a future period, whether it is a small matter or big. This action is more just for you in the sight of Allah, because it establishes stronger evidence and is the best way to remove all doubts; but if it is a common commercial transaction concluded on the spot among yourselves, there is no blame on you if you do not put it in writing. You should have witnesses when you make commercial transactions. Let no harm be done to the scribe or witnesses; and if you do so, you shall be guilty of transgression. Fear Allah; it is Allah that teaches you and Allah has knowledge of everything." Al-Qur'an 2:282