Musannaf Ibn Abi Shayba 13:1840

Abu Bakr narrated to us, he said: Abbad ibn al-Awwam narrated to us, from Yahya ibn Sa'id, from Salim: That Ibn Umar sold a slave of his for eight hundred dirhams, and the buyer found a defect in him, so he disputed with him before Uthman. He [Ibn Umar] said to him [Uthman]: "I sold him with a disclaimer (al-bara'ah)." He refused to take an oath, so Uthman returned him to him.