Ibn 'Umar reported God's Messenger as saying, "Both parties in a business transaction have a right to annul it so long as they have not separated, except in transactions which have been made subject to the right of the parties to annul them.” The version by Bukhari and Muslim has "or one of them tells the other to exercise his right” instead of "or exercise the right.”
(Bukhari and Muslim.)
A version by Muslim says, "Both parties in a business transaction have a right to annul the bargain so long as they have not separated, or when their bargain has attached to it the right to annul it, for when such a condition has been made it remains valid.”
A version by Tirmidhi says, "The two parties in a business transaction have a right to annul it so long as they have not separated, or exercise the right.”