The Messenger of Allah 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."  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ الْبَيِّعَانِ بِالْخِيَارِ مَا لَمْ يَفْتَرِقَا فَإِنْ بَيَّنَا وَصَدَقَا بُورِكَ لَهُمَا فِي بَيْعِهِمَا وَإِنْ كَذَبَا وَكَتَمَا مُحِقَ بَرَكَةُ بَيْعِهِمَا