Exodus 17:5; Exodus 17:6

5 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 your staff with which you struck the Nile, and go.

6 "Behold, I will stand before you there on the rock at Horeb; and you shall strike the rock, and water will come out of it, that the people may drink." And Moses did so in the sight of the elders of Israel.