That the Messenger of Allah ﷺ said: "When the two parties (in a deal) disagree then the seller's statement is taken as valid, and the purchaser retains the option." (Using translation from Tirmidhī 1270)
سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ إِذَا اخْتَلَفَ الْبَيِّعَانِ فَالْقَوْلُ مَا قَالَ الْبَائِعُ وَالْمُبْتَاعُ بِالْخِيَارِ