ENOfficial
It was narrated from Yazid bin 'Abdullah, from 'Abdullah bin dinar, from ibn 'Umar that he heard the Messenger of Allah (ﷺ) say: "When two people meet to engage in trade the transaction between them is not binding until they separate, unless they have chosen to conclude the transaction."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا الرَّبِيعُ بْنُ سُلَيْمَانَ بْنِ دَاوُدَ، قَالَ حَدَّثَنَا إِسْحَاقُ بْنُ بَكْرٍ، قَالَ حَدَّثَنَا أَبِي، عَنْ يَزِيدَ بْنِ عَبْدِ اللَّهِ، عَنْ عَبْدِ اللَّهِ بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، أَنَّهُ سَمِعَ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " كُلُّ بَيِّعَيْنِ لاَ بَيْعَ بَيْنَهُمَا حَتَّى يَتَفَرَّقَا إِلاَّ بَيْعَ الْخِيَارِ " .
sunnah.com