Musannaf Ibn Abi Shayba 13:1841

Abu Bakr narrated to us, he said: Jarir narrated to us, from Mughira and Ibn Shubruma, they said: Abdullah bought a slave from a man. When he took him to his house, the slave developed a fever in the cold. He disputed with him before al-Sha'bi. He said to Abdullah: "Do you have evidence that he concealed a defect from you?" He said: "I have no evidence." He said to the man: "Swear that you did not sell him with a disease." The man said: "I return the oath to Abdullah." Al-Sha'bi ruled that the oath be upon him (Abdullah), and he said: "Either you swear, or the slave is binding upon you."