(10) باب ثُبُوتِ خِيَارِ الْمَجْلِسِ لِلْمُتَبَايِعَيْنِ
Ibn 'Umar (Allah be pleased with thcm) reported Allah's Messenger (ﷺ) as saying:
When two persons enter into a transaction, each of them has the right to annul it so long as they are not separated and are together (at the place of transaction) ; or if one gives the other the right (to annul the transaction) But if one gives the other the option, the transaction is made on this condition (i. e. one has the right to annul the transaction), it becomes binding. And if they are separated after they have made the bargain and none of them annulled it, even then the transaction is binding.
Reference: Sahih Muslim 1531 c
In-book reference: Book 21, Hadith 54
USC-MSA web (English) reference(deprecated numbering scheme): Book 10, Hadith 3658