Exodus 17:9-11

Moses commanded Joshua, “Choose some men to go out and fight the army of Amalek for us. Tomorrow, I will stand at the top of the hill, holding the staff of God in my hand.” So Joshua did what Moses had commanded and fought the army of Amalek. Meanwhile, Moses, Aaron, and Hur climbed to the top of a nearby hill. As long as Moses held up the staff in his hand, the Israelites had the advantage. But whenever he dropped his hand, the Amalekites gained the advantage.