"The Messenger of Allah said: "The two parties to a transaction both have the choice who long as they have not separated or one of them says to the other: 'Decide!"' (Sahih ) (Using translation from Nasāʾī 4469)
أَنَّ رَسُولَ اللهِ ﷺ قَالَ الْبَيِّعَانِ بِالْخِيَارِ مَا لَمْ يَتَفَرَّقَا أَوْ يَقُولُ أَحَدُهُمَا لِصَاحِبِهِ اخْتَرْ