Musannaf Ibn Abi Shayba 13:656

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from Yunus, from al-Hasan, who said: If you marry an *umm al-walad* (a slave woman who has borne a child to her master) and she gives birth, then her child is in the same status as she is.