Sunan Ibn Majah, Chapter: The Chapters on Manumission (of Slaves)

I said to Kab bin Murrah, tell us a Hadith from the Messenger of Allah (saw), but be careful. He said: I heard the Messenger of Allah (saw) say: "Whoever frees a Muslim man, he will be his ransom from the Fire; each of his bones will suffice (as a ransom) for each of his bones. Whoever frees two Muslim women, they will be his ransom from the Fire; each of their two bones will suffice (as a ransom) for each of his bones." Daif