The Messenger of Allah ﷺ said, "The two parties to a sale each have the right of choice until they part, unless it is a sale with a stipulated option."Nafi sometimes added, "or one of them says to the other, 'Choose.'"
حدثنا إسماعيل أخبرنا أيوب عن نافع
قال رسول الله ﷺ البيعان بالخيار حتى يتفرقا أو يكون بيع خيار قال وربما قال نافع أو يقول أحدهما للآخر اختر
Its chain of transmission is sahih. It has already passed as no. 393 through the route of Malik from Nafi. It was also narrated by the two shaykhs (Bukhari and Muslim), as noted in Muntaqa 2880. Shafii narrated it in Al-Umm 3:3 from Malik and from Ibn Jurayj, both of them from Nafi, and he also narrated it from Sufyan bin Uyayna, from Abdullah bin Dinar, from Ibn Umar. He elaborated at length in explaining it and in refuting those who disagreed with it and did not act upon it, meaning the option of the session (khiyar al-majlis). He likewise refuted Malik with this hadith in the book Ikhtilaf Malik wal-Shafii, appended to Al-Umm 7:204, and it will come again through the route of Sufyan bin Uyayna from Abdullah bin Dinar at no. 4566.The two parties to a sale (al-bayyian) are the seller and the buyer. Each of them is called "al-bay" with a fatha on the ba and a doubled, kasra-marked ya, and also "baa" (seller). So said Ibn Athir.