Exodus 17:5-6

Then the LORD said to Moses, “Pass before the people and take with you some of the elders of Israel; and take in your hand the staff with which you struck the Nile, and go. Behold, I will stand before you there on the rock at Horeb; there you shall strike the rock, and water will come out of it, so that the people may [have something to] drink.” And Moses did so in the sight of the elders of Israel. [1 Cor 10:4]