It was narrated that Hakim bin Hizam said: The Messenger of Allah (ﷺ) said: "The two parties to a transaction have the choice so long as they have not separated. If they are honest and open, their transaction will be blessed, but if they tell lies and conceal anything the blessing of their transaction will be lost."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا أَبُو الأَشْعَثِ، عَنْ خَالِدٍ، قَالَ حَدَّثَنَا سَعِيدٌ، - وَهُوَ ابْنُ أَبِي عَرُوبَةَ - عَنْ قَتَادَةَ، عَنْ صَالِحٍ أَبِي الْخَلِيلِ، عَنْ عَبْدِ اللَّهِ بْنِ الْحَارِثِ، عَنْ حَكِيمِ بْنِ حِزَامٍ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " الْبَيِّعَانِ بِالْخِيَارِ مَا لَمْ يَفْتَرِقَا فَإِنْ بَيَّنَا وَصَدَقَا بُورِكَ لَهُمَا فِي بَيْعِهِمَا وَإِنْ كَذَبَا وَكَتَمَا مُحِقَ بَرَكَةُ بَيْعِهِمَا " .
sunnah.com