Musannaf Ibn Abi Shayba 13:899

Abu Bakr narrated to us, he said: Umar bin Harun narrated to us, from Ibn Jurayj, from Ata, who said: I said to him: Two men disagree regarding a sale, and there is no evidence between them. He said: The sale is rescinded if they do not reach an agreement, if they have no evidence.