Exodus 17:9-16

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. Now when Moses held up his hand, Israel prevailed, and when he lowered his hand [due to fatigue], Amalek prevailed. But Moses’ hands were heavy and he grew tired. So they took a stone and put it under him, and he sat on it. Then Aaron and Hur held up his hands, one on one side and one on the other side; so it was that his hands were steady until the sun set. So Joshua overwhelmed and defeated Amalek and his people with the edge of the sword. Then the LORD said to Moses, “Write this in the book as a memorial and recite it to Joshua, that I will utterly wipe out the memory of Amalek [and his people] from under heaven.” [1 Sam 15:2-8] And Moses built an altar and named it The LORD Is My Banner; saying, “The LORD has sworn [an oath]; the LORD will have war against [the people of] Amalek from generation to generation.”