Exodus 17:8-10

Then Amalek came and fought with Israel at Rephidim. So Moses said to Joshua, “Choose for us men, and go out and fight with Amalek. Tomorrow I will stand on the top of the hill with the staff of God in my hand.” So Joshua did as Moses told him, and fought with Amalek, while Moses, Aaron, and Hur went up to the top of the hill.