Narrated Abdullah ibn Mas'ud:
Muhammad ibn al-Ash'ath said: Al-Ash'ath bought slaves of booty from Abdullah ibn Mas'ud for twenty thousand (dirhams. Abdullah asked him for payment of their price. He said: I bought them…
'Abdullah said:
"I heard the Messenger of Allah (ﷺ) 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.'''