Musannaf Ibn Abi Shayba 13:655

Abu Bakr narrated to us, he said: Ibn Mushir and Ibn Abi Za’idah narrated to us, from Dawud, from al-Sha’bi: Regarding the children of the *umm al-walad* (a slave woman who has borne a child to her master): they are emancipated by her emancipation, and they remain in slavery by her remaining in slavery.