Musannaf Ibn Abi Shaybah 35068 — What they said on a man captured

Qatadah (may Allah have mercy on him) said: Sayyiduna Ali (may Allah be pleased with him) was asked about a mukatab slave (one who has contracted to buy his freedom) whom the enemy had taken captive and then a Muslim man bought him: What is the ruling on him? He said: "If his master wishes, he may redeem him. The slave then stays with his master on the condition that he pays the remaining amount of his contract, and the master will have his wala' (right of clientage). And if he does not like that, the slave stays with the one who bought him in this same state."