An-Nahl 16:94

Executing an agreement on oath is the final shape of a firm agreement. From this point of view, all agreements are covered by this verse. If Muslims enter into transactions involving agreements with others and thereafter, without any real reason and only for the sake of self-interest, break them, this will result in destroying the moral credibility of Muslims in general. This will create an atmosphere such as will discourage others from adopting the way of God. Ibn Kathir writes that when a rejecter of Islam sees that a Muslim has entered into an agreement, but goes against it, he will have no faith in the religion of Islam and will abstain from embracing the religion of God. The act of breaking an agreement against the principles of Islamic law inevitably occurs when one partner to it sees that he will receive certain worldly benefits by doing so. But a believer’s view is Hereafter-oriented. Whenever it is the self which makes a move to break the agreement, the person concerned curbs his self by saying that there may be some worldly benefit in breaking it, but he will gain no advantage thereby in the Hereafter. And the advantage of the Hereafter is definitely greater than any worldly benefit.