Musannaf Ibn Abi Shayba 13:678

Abu Bakr narrated to us, he said: Ad-Dahhak bin Makhlad narrated to us, from Ibn Jurayj, from Abu az-Zubayr, from Jabir, who said: I do not see the children of the *mudabbarah* (a slave woman promised freedom upon her master's death) except as being in the same status as their mother.