Musannaf Ibn Abi Shayba 9:369

Ibn ‘Ulayyah narrated to us, from Ibn Jurayj, who said: ‘Ikrimah informed me, from Mujahid, that he said regarding: "And your stepdaughters who are under your guardianship (born) of your wives unto whom you have gone in," He intended by both of them: combining them [in marriage].