Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever frees a believing slave, Allah Almighty will free every limb of his from Hell in return for a limb of that slave. He frees a hand for a hand, a foot for a foot and private parts for private parts." Ali bin Husayn (may Allah have mercy on him) said to the narrator: Did you hear this from Sayyiduna Abu Hurayrah (may Allah be pleased with him)? He said: Yes. Ali (may Allah have mercy on him) said: Call Mutarrif for me, and he was one of his most able slaves. When he stood before him, he said: You are free for the pleasure of Allah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الوصايا / 12596