Musannaf Ibn Abi Shayba 9:345

Abu Usama narrated to us, from Mujalid, from Amir, who said: A man from Hamdan had a slave girl and her daughter, and he used to have intercourse with both of them. Ali was informed of that, so he asked him. He said: "Yes." Ali said to him: "If one verse has made them lawful for you and another has made them unlawful for you, then I possess them—the daughter is forbidden."