Muwatta Imam Malik (Riwayat Ibn al-Qasim)

And with this chain (it is narrated from Sayyiduna Abu Hurairah, may Allah be pleased with him) that the Messenger of Allah, peace and blessings be upon him, said: "The best charity is a select she-camel that gives plenty of milk and is close to giving birth, and it is given as a gift to someone; and the gift of that special goat which fills one vessel with (milk) in the morning and another vessel in the evening."