Hadith 4480
أَخْبَرَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " الْبَيِّعَانِ بِالْخِيَارِ مَا لَمْ يَتَفَرَّقَا أَوْ يَكُونَ بَيْعُهُمَا عَنْ خِيَارٍ " .
It was narrated from Sufyan, from 'Abdullah bin Dinar, from Ibn 'Umar, from the Prophet who said:
"Two traders have the choice as long as they have not separated, or, they have chosen to conclude the transaction."
Reference : Sunan an-Nasa'i 4480
In-book reference : Book 44, Hadith 32