Abu Dawud
Wages
Book Number: 017 / Hadith Number: 3449
Narated By Abdullah ibn Amr ibn al-'As : The Prophet (pbuh) said: Both parties in a business transaction have a right to annul it so long as they have not separated unless it is a bargain with the option to annul is attached to it; and it is not permissible for one of them to separate from the other for fear that one may demand that the bargain be rescinded.