Exodus 17:8-13

8After this, the Amalekites came and attacked the Israelites at Rephidim. 9So Moses said to Joshua, “Choose some of our men and go out to fight the Amalekites. Tomorrow I will stand on the hilltop with the staff of God in my hand.”

10Joshua did as Moses had instructed him and fought against the Amalekites, while Moses, Aaron, and Hur went up to the top of the hill.

11As long as Moses held up his hands, Israel prevailed; but when he lowered them, Amalek prevailed. 12When Moses’ hands grew heavy, they took a stone and put it under him, and he sat on it. Then Aaron and Hur held his hands up, one on each side, so that his hands remained steady until the sun went down.

13So Joshua overwhelmed Amalek and his army with the sword.