Sayyiduna Abdullah bin Umar (may Allah be pleased with them) narrated that the Messenger of Allah (peace and blessings be upon him) said: The buyer and the seller both have the option (to cancel the transaction) as long as they have not separated from each other, except in the case of a sale with a stipulated option.
Hadith Referenceاللؤلؤ والمرجان / كتاب البيوع / 978
Hadith Gradingمحدثین:«صحیح»
Hadith Takhrij«صحیح، أخرجه البخاري في: 34 كتاب البيوع: 44 باب البيعان بالخيار ما لم يتفرقا»
Brief Explanation
That is, when the seller, after the sale, grants the buyer the option, and the buyer says, “I confirm (execute) the sale.” And this sale is different from the one in which the condition of option was stipulated from the outset. (Raaz)