Musannaf Ibn Abi Shayba 9:356

Abu Bakr ibn Ayyash narrated to us, from Abd al-Aziz ibn Rufay, who said: I asked Ibn al-Hanafiyyah about a man who has two slave women; may he have intercourse with both of them? He said: "A verse made them lawful, and a verse made them unlawful." Then I went to Ibn al-Musayyib, and he said the same as what Muhammad [Ibn al-Hanafiyyah] said. Then I asked Ibn Munabbih, and he said: "I bear witness that it is in what Allah revealed to Moses that he is cursed who joins between two sisters." He said: "He did not distinguish for us between free women or slave women." He said: So I returned to Ibn al-Musayyib and informed him, and he said: "Allah is the Greatest."