Musnad Ahmad 30:1580

Yunus narrated to us, Fulayh narrated to us, from Muhammad ibn Abdullah ibn al-Husayn, from Ubaydullah ibn Sabihah, from Abu Hurayrah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The best of charity is the *minihah* (loaning a milking animal). It goes out in the morning with a reward, and it returns in the evening with a reward. The *minihah* of a she-camel is like the freeing of a red slave, and the *minihah* of a sheep is like the freeing of a black slave."