Musannaf Ibn Abi Shaybah

Ibrahim (may Allah have mercy on him) said regarding the person who, in his terminal illness, freed his slave and then died, and he also had a debt upon him, and besides this slave he had no other wealth: he said, the slave will strive to the extent of his value; if his value is more than the debt, then he will strive for the creditors to the extent of their debt, and whatever remains will be considered; then two-thirds of it will belong to the heirs and one-third will be his (i.e., for the bequest).