Sunan an Nasai 4467
The Book of Financial Transactions
أَخْبَرَنَا مُحَمَّدُ بْنُ عَلِيٍّ الْمَرْوَزِيُّ، قَالَ حَدَّثَنَا مُحْرِزُ بْنُ الْوَضَّاحِ، عَنْ إِسْمَاعِيلَ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " الْمُتَبَايِعَانِ بِالْخِيَارِ مَا لَمْ يَفْتَرِقَا إِلاَّ أَنْ يَكُونَ الْبَيْعُ كَانَ عَنْ خِيَارٍ فَإِنْ كَانَ الْبَيْعُ عَنْ خِيَارٍ فَقَدْ وَجَبَ الْبَيْعُ " .
it was narrated from Ismail, from Nafi, that Ibn 'Umar said:"The Messenger of Allah said: 'The two parties to a transaction both have the choice so long as they have not separated, unless they have both chosen to conclude they transaction. If they have both chosen to conclude the transaction, then the transaction is binding." (Sahih)
Grading: Abu Ghuddah: Sahih · Al-Albani: Sahih · Zubair Ali Zai: Isnaad Sahih
Text from the public-domain hadith-api dataset. Numbering follows that dataset and can differ by a few from some printed editions — check the wording, not only the number.