Narrated Ibn 'Umar (RA):

Allah's Messenger (ﷺ) said: "Both parties in a business transaction have a right to annul the transaction, so long as they have not separated and remain together; or one of them gives the other the choice (to conclude or annul the transaction); so, if one of them gives the other the choice (to conclude or annul the transaction) and then they make the transaction accordingly, the transaction then becomes binding; or if they separate after having made the transaction and none of them has annulled it, the transaction then becomes binding." [Agreed upon, and the wording is Muslim's].

وَعَنْ اِبْنِ عُمَرَ ‏-رَضِيَ اَللَّهُ عَنْهُمَا‏-, عَنْ رَسُولِ اَللَّهِ ‏- صلى الله عليه وسلم ‏-قَالَ: { إِذَا تَبَايَعَ اَلرَّجُلَانِ, فَكُلُّ وَاحِدٍ مِنْهُمَا بِالْخِيَارِ مَا لَمْ يَتَفَرَّقَا وَكَانَا جَمِيعاً, أَوْ يُخَيِّرُ أَحَدُهُمَا اَلْآخَرَ, فَإِنْ خَيَّرَ أَحَدُهُمَا اَلْآخَرَ فَتَبَايَعَا عَلَى ذَلِكَ فَقَدَ وَجَبَ اَلْبَيْعُ, وَإِنْ تَفَرَّقَا بَعْدَ أَنْ تَبَايَعَا, وَلَمْ يَتْرُكْ وَاحِدٌ مِنْهُمَا اَلْبَيْعَ فَقَدْ وَجَبَ اَلْبَيْعُ } مُتَّفَقٌ عَلَيْهِ, وَاللَّفْظُ لِمُسْلِمٍ [1]‏ .‏