Imam Malik's Muwatta, Chapter: Business Transactions

Yahya related to me from Malik from Nafi from Abdullah ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, said, "Both parties in a business transaction have the right of withdrawal as long as they have not separated, except in the transaction called khiyar." Malik said, "There is no specified limit nor any matter which is applied in this case according to us."