Musnad Ahmad 788:139

Sufyan ibn 'Uyaynah narrated to us, Shu'bah al-Kufi narrated to us, he said: We were with Abu Burdah ibn Abi Musa, and he said: "O my son, shall I not narrate to you a hadith that my father narrated to me, from the Messenger of Allah, may Allah bless him and grant him peace, who said: 'Whoever frees a slave, Allah the Mighty and Majestic will free, for every limb of that slave, a limb of his own from the Fire.'"