Musannaf Ibn Abi Shayba 13:2651

Abu Bakr narrated to us, he said: Ibn Mubarak narrated to us, from Ibn Jurayj, he said: Ibn Abi Mulaykah informed me that a woman entered into a *kitabah* (contract of manumission) and gave birth to two children during her *kitabah*. Then she died. Abdullah ibn al-Zubayr was asked about that, and he said: "If they remain upon the *kitabah* of their mother, then that is for them; and when they pay it off, they shall be freed."