سنن أبي داود

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 for ten thousand (dirhams). Abdullah said: Appoint a man who may adjudicate between me and you. Al-Ash'ath said: (I appoint) you between me and yourself. Abdullah said: I heard the Messenger of Allah (ﷺ) say: If both parties in a business transaction differ (on the price of an article), and they have witness between them, the statement of the owner of the article will be accepted (as correct) or they may annul the transaction.