(45) باب إِذَا خَيَّرَ أَحَدُهُمَا صَاحِبَهُ بَعْدَ الْبَيْعِ فَقَدْ وَجَبَ الْبَيْعُ
Narrated Ibn `Umar:
Allah's Messenger (ﷺ) said, "Both the buyer and the seller have the option of canceling or confirming the bargain, as long as they are still together; and unless they separate or one of them gives the other the option of keeping or returning the things and a decision is concluded then, in which case the bargain is considered final. If they separate after the bargain and none of them has rejected it, then the bargain is rendered final."
Reference: Sahih al-Bukhari 2112
In-book reference: Book 34, Hadith 65
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 34, Hadith 325