Sahih al-Bukhari, Volume 3, Book 34, Hadith 326 (USC-MSA) ⓘ
Narrated Ibn `Umar: The Prophet said, "No deal is settled and finalized unless the buyer and the seller separate, except if the deal is optional (whereby the validity of the bargain depends on the stipulations agreed upon).
حَدَّثَنَا مُحَمَّدُ بْنُ يُوسُفَ، حَدَّثَنَا سُفْيَانُ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " كُلُّ بَيِّعَيْنِ لاَ بَيْعَ بَيْنَهُمَا حَتَّى يَتَفَرَّقَا، إِلاَّ بَيْعَ الْخِيَارِ " .
also referenced under: Book 34, Hadith 66 (In-Book) & Hadith 2113 (DarusSalam)