Musannaf Ibn Abi Shayba 26:480

Waki’ narrated to us, he said: Sufyan narrated to us, from Mansur, from Ibrahim, who said regarding a man who enters into a *kitabah* (emancipation contract) with his slave, then dies and leaves behind children, both male and female: The wealth is between them according to their shares, and the *wala’* (right of patronage) belongs to the males to the exclusion of the females.