Qasim says that once there was a dispute over the price of something between Sayyiduna Ibn Mas'ud and Sayyiduna Ash'ath (may Allah be pleased with them both). One person was saying ten and the other twenty. Sayyiduna Ibn Mas'ud (may Allah be pleased with him) said: Appoint someone as an arbitrator between you and me. He said: I appoint you as the arbitrator. Sayyiduna Ibn Mas'ud (may Allah be pleased with him) said: Then I will give the same decision as the Prophet (peace and blessings of Allah be upon him) gave, that "If there is a dispute between the seller and the buyer (the one who buys and the one who sells), and neither has any witnesses, then the statement of the seller will be accepted, or both should conduct a new transaction."