Musannaf Ibn Abi Shayba 26:518

'Abd al-Rahman ibn Mahdi narrated to us, from Hammad ibn Salamah, from Qays ibn Sa'd, from Mujahid; and from Qatadah, from Humayd ibn 'Abd al-Rahman, and 'Ikrimah ibn Khalid, from Yazid ibn 'Abd al-Malik: They said: "Whatever she gives birth to while she is a slave, the *wala'* (patronage) belongs to the masters of the mother. And whatever she gives birth to while she is free, the *wala'* belongs to the masters of the father."