Tertullian

For the people, after crossing the sea, and being carried about in the desert during forty years, although they were there nourished with divine supplies, nevertheless were more mindful of their belly and their gullet than of God. Thereupon the Lord, driven apart into desert places after baptism, showed, by maintaining a fast of forty days, that the man of God lives "not by bread alone," but "by the word of God; " and that temptations incident to fulness or immoderation of appetite are shattered by abstinence.