Deuteronomy 8:15-16

He led you through the great and terrible wilderness, with its fiery serpents and scorpions and thirsty ground where there was no water; it was He who brought water for you out of the flinty rock. He fed you manna in the wilderness, [a substance] which your fathers did not know, so that He might humble you [by dependence on Him] and that He might test you, to do good [things] for you at the end.