Sunan an-Nasa'i 4482
It was narrated from Al- Hasan from Samurah, who said:
"The Messenger of Allah said;" Two traders have the choice as long as they have not separated, or until they reach a deal that suits both of th4em or that is satisfactory (to both)"
أَخْبَرَنِي مُحَمَّدُ بْنُ إِسْمَاعِيلَ بْنِ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا يَزِيدُ، قَالَ أَنْبَأَنَا هَمَّامٌ، عَنْ قَتَادَةَ، عَنِ الْحَسَنِ، عَنْ سَمُرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ الْبَيِّعَانِ بِالْخِيَارِ مَا لَمْ يَتَفَرَّقَا وَيَأْخُذْ أَحَدُهُمَا مَا رَضِيَ مِنْ صَاحِبِهِ أَوْ هَوِيَ ‏"‏ ‏.‏