Sunan an-Nasa'i 4480
سنن النسائي#4480Sahihأَخْبَرَنَا 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
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 44:32