"I heard the Messenger of Allah say: 'If the two parties to a transaction disagree, and neither of them has any proof, then it is as the owner of the goods says, or they may cancel it.''' (Using translation from Nasāʾī 4648)   

قَالَ رَسُولُ اللهِ ﷺ إِذَا اخْتَلَفَ الْبَيِّعَانِ وَلَيْسَ بَيْنَهُمَا بَيِّنَةٌ فَالْقَوْلُ مَا يَقُولُ صَاحِبُ السِّلْعَةِ أَوْ يَتَرَادَّانِ  

[Machine] I heard the Messenger of Allah ﷺ saying, "When both parties to a transaction differ, the sale is valid as long as they are clear about what is being sold, and there is no discrepancy in their words. The statement of the seller is considered, or they may retract the sale."  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ «الْبَيِّعَانِ إِذَا اخْتَلَفَا وَالْبَيْعُ قَائِمٌ بِعَيْنِهِ وَلَيْسَ بَيْنَهُمَا بَيِّنَةٌ فَالْقَوْلُ مَا قَالَ الْبَائِعُ أَوْ يَتَرَادَّانِ الْبَيْعَ»