Exodus 17:8-10

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