Musannaf Ibn Abi Shaybah

Hazrat Salim narrates that Hazrat Ibn Umar (may Allah be pleased with them both) sold a slave for eight hundred dirhams. Later, the buyer found a defect in him and brought the case before Hazrat Uthman (may Allah be pleased with him). Hazrat Uthman (may Allah be pleased with him) asked Hazrat Ibn Umar (may Allah be pleased with them both) about this matter. He replied that he had sold him with a declaration of exemption from defects. Hazrat Uthman (may Allah be pleased with him) then said to Hazrat Ibn Umar (may Allah be pleased with them both): "Do you swear that at the time you sold him, you had no knowledge of any defect in him?"