Musannaf Ibn Abi Shayba 17:1406

Ibn Mahdi narrated to us, from Sufyan, from Sa’d ibn Yusuf ibn Ya’qub, who said: They said to Tawus regarding a slave of his. He said: "He has no wealth for me to manage for him, nor is he righteous for me to marry him off." And he used to dislike beating, and he would say: "The shackle."