Ibn Hibban

Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates this statement of the Prophet Muhammad (peace be upon him): "When two men make a transaction, each of them has the right (to cancel the transaction) as long as they have not separated from each other and remain together, or until one of them gives the other (the right to cancel the transaction later). If one of them gives the other the right of option and they make the transaction on that condition, then the transaction is finalized. And if, after finalizing the transaction, they separate and neither of them has abandoned the sale, then the sale becomes binding."