Musnad Ahmad 30:2434

Yahya ibn Sa'id narrated to us, he said: 'Abdullah ibn Sa'id ibn Abi Hind narrated to us, he said: Isma'il ibn Abi Hakim narrated to us, from Sa'id ibn Marjanah, he said: I heard Abu Hurairah saying: The Messenger of Allah, may Allah bless him and grant him peace, said: "Whoever frees a slave, Allah will free, for every limb of his, a limb of his from the Fire."