Exodus 17:5-6

The LORD said to Moses, “Walk out in front of the people. Take your staff, the one you used when you struck the water of the Nile, and call some of the elders of Israel to join you. I will stand before you on the rock at Mount Sinai. Strike the rock, and water will come gushing out. Then the people will be able to drink.” So Moses struck the rock as he was told, and water gushed out as the elders looked on.