Exodus 17:3, 6

And the people thirsted there for water; and the people murmured against Moses, and said, Wherefore hast thou brought us up out of Egypt, to kill us and our children and our cattle with thirst?

Behold, I will stand before thee there upon the rock in Horeb; and thou shalt smite the rock, and there shall come water out of it, that the people may drink. And Moses did so in the sight of the elders of Israel.