Musannaf Ibn Abi Shayba 13:663

Abu Bakr narrated to us, he said: Abu Mu'awiyah narrated to us, from Yahya ibn Sa'id, from Sa'id ibn al-Musayyib, he said: The child of the *mudabbarah* (a slave woman whose freedom is promised upon the death of her master) is in the same status as her.