Bayhaqi 21720 — The mukatab granting a contract of manumission

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.