ENOfficial
It was narrated from Sufyan, from 'Amr bin Dinar, from Ibn 'Umar, who said: the Messenger of Allah (ﷺ) said: "When two people meet to engage in trade, the transaction between them is not binding until they separate, unless they have chosen to concluded the transaction.
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا عَبْدُ الْحَمِيدِ بْنُ مُحَمَّدٍ، قَالَ حَدَّثَنَا مَخْلَدٌ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ عَمْرِو بْنِ دِينَارٍ، عَنِ ابْنِ عُمَرَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " كُلُّ بَيِّعَيْنِ لاَ بَيْعَ بَيْنَهُمَا حَتَّى يَتَفَرَّقَا إِلاَّ بَيْعَ الْخِيَارِ " .
sunnah.com