Narrated `Abdullah bin `Umar: Allah's Apostle said, "Both the buyer and the seller have the option of canceling or confirming a bargain unless they separate, or the sale is optional." (See Hadith No.320).
Hadith ReferenceSahih Bukhari / The Book of Sales (Bargains) / Hadith: 2111
Hadith Gradingمحدثین:أحاديث صحيح البخاريّ كلّها صحيحة