Musnad Ahmad 652:57

Zayd ibn al-Hubab narrated to us, Husayn ibn Waqid narrated to us, Simak ibn Harb narrated to me, from al-Nu’man ibn Bashir, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Whoever grants a *maniha* (a gift of a milking animal) of silver or gold, or provides milk to drink, or guides [someone] along a path, it is like the freeing of a slave."