Sahih Bukhari
Sales and Trade
Volume: 003 / Book Number: 034 / Hadith Number: 320
Narrated Ibn 'Umar:
The Prophet said, "The buyer and the seller have the option to cancel or confirm the bargain before they separate from each other or if the sale is optional." Nafi said, "Ibn 'Umar used to separate quickly from the seller if he had bought a thing which he liked."