Exodus 17:9-11

17:9 So Moses said to Joshua, “Choose some of our men and go out, fight against Amalek. Tomorrow I will stand on top of the hill with the staff of God in my hand.”

17:10 So Joshua fought against Amalek just as Moses had instructed him;and Moses and Aaron and Hur went up to the top of the hill. 17:11 Whenever Moses would raise his hands, then Israel prevailed, but whenever he would rest his hands, then Amalek prevailed.