Musannaf Ibn Abi Shayba 28:334

'Abdah ibn Sulayman narrated to us, from Ibn Abi 'Arubah, from Qatadah, who said: Ali was asked about a *mukātab* (a slave who has a contract of manumission) whom the enemy captured, then a man from the Muslims bought him. He said: If his master wishes to redeem him, he shall remain with him according to what remains of his *mukātabah* (contract), and the *walā'* (right of inheritance/patronage) shall belong to him. And if he dislikes that, he shall remain with the one who bought him in this same state.