Musannaf Ibn Abi Shayba 13:849

Abu Bakr narrated to us, he said: Abbad bin al-Awwam narrated to us, from Yahya bin Sa'id, from Salim: That Ibn Umar sold a slave for eight hundred dirhams, and the buyer found a defect in him, so he disputed with him before Uthman. He said: So Uthman asked him, and he said: "I sold him with [a condition of] immunity." He said: "Will you swear to him that you sold him while there was no defect in him that you knew of?"