It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "The blood money of a mukatab (a slave who has contracted to buy his freedom) is the blood money of a free man in proportion to the part of him that has been freed, and the blood money of a slave in proportion to the part of him that remains enslaved."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11941