It was said to Sayyiduna Ka'b bin Murrah or Murrah bin Ka'b (may Allah be pleased with him): Narrate to us a hadith that you heard from the Messenger of Allah (peace and blessings be upon him), may Allah bless you, and be careful. He said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whichever Muslim frees a Muslim, Allah will free him from Hell, bone for bone. Whichever Muslim frees two women, freeing them is his protection from Hell, every two of their bones (counting) for one of his bones. And whichever woman frees a Muslim woman will gain freedom from Hell, her bone for her bone."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العتق / 21309