Musnad Ahmad 814:2

Hushaym narrated to us, Ali ibn Zayd said: We were informed by Zurarah ibn Awfa, from Malik ibn al-Harith, a man from among them, that he heard the Prophet, peace and blessings of Allah be upon him, say: "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 will be his release from the Fire; for every limb of his, a limb of his will be recompensed."