Musannaf Ibn Abi Shayba 28:783

Humaid narrated to us, from Hassan bin Salih, who said: I asked 'Ata' bin al-Sa'ib about His saying: "And know that anything you obtain of war booty, then indeed for Allah is one fifth of it," and about this verse: "What Allah restored to His Messenger." He said: I said, "What is *al-fay'* and what is *al-ghanimah*?" He said: "If the Muslims overcome the polytheists and their land, and they take them by force, then whatever they take of their wealth that they have overcome is *ghanimah*. As for the land, it is *fay'*, and this *sawad* (cultivated land) of ours is *fay'*."