Musannaf Ibn Abi Shayba 13:703

Abu Bakr narrated to us, he said: Abu Khalid and Abu Mu'awiyah narrated to us, from Yahya ibn Sa'id, from Sa'id ibn al-Musayyib, he said: The *mudabbarah* (a slave woman promised freedom upon her master's death), her master shall not sell her, nor shall he marry her off, nor shall he give her away as a gift. And her child is in her status.