Musnad Ahmad 744:1

Hashim narrated to us, he said: Ali bin Zaid informed us, from Zurarah bin Awfa, from Malik bin al-Harith, a man from among them, that he heard the Prophet, peace and blessings of Allah be upon him, saying: "Whoever takes an orphan between two Muslim parents into his food and drink until he becomes independent of him, Paradise becomes mandatory for him, absolutely. And whoever frees a Muslim person, it is his release from the Fire; for every limb of his, a limb of his is freed from the Fire."