Ibn Umar (may Allah be pleased with them both) narrated that the Messenger of Allah (ﷺ) said: "When two parties engage in a sale, each of them has the option (to cancel or confirm the sale) as long as they have not separated, or unless they have chosen the option of finalizing the sale." Nafi' said that when Ibn Umar (may Allah be pleased with them both) would make a sale and wanted to finalize it, he would walk a little away from that place and then return.
Hadith Referenceمسند الإمام الشافعي / كتاب البيوع / 1373