Musannaf Ibn Abi Shaybah 33034 — A man who appoints his slave

It is narrated from Mughirah that Ibrahim said, concerning a man who made his mukatab slave (one contracted to buy his freedom) responsible for his bequest, and afterwards the mukatab said, "I have spent the payment of my contract on my master's household," that the mukatab will be believed and this is valid. It is also permissible for a man to entrust his bequest to his slave, but if the slave later says, "I have made myself mukatab," or says, "I have sold myself," this is not permissible for him.