Musannaf Ibn Abi Shayba 13:2200

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ibn Jurayj, who said: Ata was asked about a man who was granted a contract of manumission (kitabah), and his masters stipulated upon him that: "We have a share of your inheritance." He said: "The condition of Allah is before their condition."