Musannaf Ibn Abi Shayba 26:520

'Abd al-Wahhab ibn 'Ata' narrated to us, from Ibn Jurayj, who said: I said to 'Ata': A man married a free woman, then she gave birth, then the slave was emancipated. To whom does the wala' (patronage) of his child belong? He said: The wala' of his child belongs to the family of their mother.