The mukatab granting a contract of manumission and freeing a slave

Ibn Jurayj (may Allah have mercy on him) said: I said to Ata' (may Allah have mercy on him): A mukatab had a slave, and he made a contract of manumission with him. Then he died; to whom does his inheritance go? He said: Those before (you) used to say: It belongs to the one who made the contract with him, who uses it to help pay his own contract.

Khalid bin Abi Imran (may Allah have mercy on him) says: I asked Qasim and Salim (may Allah have mercy on them both) about a mukatab who pays half of his contract, then the mukatab makes a contract of manumission with a slave of his own; then both of them strive together, and the mukatab's slave pays off his contract, then the first of them becomes unable to pay. Is he (the second) returned to slavery, or is his manumission valid by what he paid to his master? They both said: If the master of the first of them had given him permission to make the contract with him, then there is no claim against him; otherwise he has the same status as him.