It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "When two parties make a transaction, both have the option to cancel the sale as long as they have not separated, or unless they have mutually agreed to forgo the option in their transaction; if that is the case, then the sale is finalized." Nafi‘ (may Allah have mercy on him) says that when Ibn Umar (may Allah be pleased with them both) made a transaction with someone and had not given the option (of cancellation), he wished that the other person would not demand a return of the sale. So Ibn Umar (may Allah be pleased with them both) would walk a little and then return to him.
Hadith Referenceالسنن المأثورة / باب في البيوع / 234
Hadith Takhrijصحیح مسلم، البيوع، باب ثبوت خيار المجلس للمتبايعين، رقم: 1531