Exodus 17:7

Moses cried to the LORD, saying, “What shall I do with these people? They are almost ready to stone me.”

The LORD said to Moses, “Walk on before the people, and take the elders of Israel with you, and take the rod in your hand with which you struck the Nile, and go.

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

Then Amalek came and fought with Israel in Rephidim.

Moses said to Joshua, “Choose men for us, and go out to fight with Amalek. Tomorrow I will stand on the top of the hill with God’s rod in my hand.”

So Joshua did as Moses had told him, and fought with Amalek; and Moses, Aaron, and Hur went up to the top of the hill.