Musannaf Ibn Abi Shayba 17:1386

'Affan narrated to us, he said: Hammad bin Salamah narrated to us, from Abu Ja'far al-Khatmi, that his father asked Sa'id bin al-Musayyib—or he said: He sent a freed slave of his, and I was with him—asking him: "For what should a man strike his orphan?" He said: "For what should a man strike his child?" Abu Ja'far said: And Muhammad bin Ka'b was asked, and he said the same.