Deuteronomy 8:3

And he humbled thee and suffered thee to hunger, Exodus 16:2, and fed thee with manna, Exodus 16:12, which thou knewest not, neither did thy fathers know, and the very fact that God was able to keep them alive without the food ordinarily demanded by men was intended to keep them humble; that He might make thee know that man doth not live by bread only, but by every word that proceedeth out of the mouth of the Lord doth man live. For the maintenance of life in His creatures the Lord is not bound to the food upon which men, by His order, must depend, but He has ways and means to sustain life by the direct exercise of His almighty power, if He so chooses. In this sense Jesus quoted this passage when He was tempted by the devil in the wilderness, Matthew 4:4.