Narrated by:Al-Laith from Nafi from Ibn 'Umar who said
It was narrated from Al-Laith from Nafi from Ibn 'Umar who said:"The Messenger of Allah said: 'The two parties to a transaction both have the choice so long as they have not separated or they have chosen to conclude the transaction.' Or perhaps Nafi said: "Or one of them has said to the other: 'Decide! (Sahih )
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الْبَيِّعَانِ بِالْخِيَارِ حَتَّى يَفْتَرِقَا أَوْ يَكُونَ بَيْعَ خِيَارٍ " . وَرُبَّمَا قَالَ نَافِعٌ " أَوْ يَقُولَ أَحَدُهُمَا لِلآخَرِ اخْتَرْ " .
Nesai
The Book of Financial Transactions • Hadith 4471