Sahih Muslim Book - 21, Hadith - 3855

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ حَدَّثَنَا لَيْثٌ ح وَحَدَّثَنَا مُحَمَّدُ بْنُ رُمْحٍ أَخْبَرَنَا اللَّيْثُ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ عَنْ رَسُولِ اللَّهِ -صلى الله عليه وسلم- أَنَّهُ قَالَ « إِذَا تَبَايَعَ الرَّجُلاَنِ فَكُلُّ وَاحِدٍ مِنْهُمَا بِالْخِيَارِ مَا لَمْ يَتَفَرَّقَا وَكَانَا جَمِيعًا أَوْ يُخَيِّرُ أَحَدُهُمَا الآخَرَ فَإِنْ خَيَّرَ أَحَدُهُمَا الآخَرَ فَتَبَايَعَا عَلَى ذَلِكَ فَقَدْ وَجَبَ الْبَيْعُ وَإِنْ تَفَرَّقَا بَعْدَ أَنْ تَبَايَعَا وَلَمْ يَتْرُكْ وَاحِدٌ مِنْهُمَا الْبَيْعَ فَقَدْ وَجَبَ الْبَيْعُ ».

It was narrated from Ibn 'Umar that the Prophet (s.a.w) said: "When two men enter into a transaction, each one of them has the option (of canceling) so long as they have not parted and are still together. But if one of them gives the other the choice to decide, then they agree on a deal, then it becomes binding. If they part after that and neither of them canceled it, then the transaction becomes binding."