Exodus 17:11-14

11And it came to pass, when Moses held up his hand, that Israel prevailed: and when he let down his hand, Amalek prevailed. 12But Moses’ hands were heavy; and they took a stone, and put it under him, and he sat on it; and Aaron and Hur held up his hands, the one on the one side, and the other on the other side; and his hands were steady until the going down of the sun. 13And Joshua overcame Amalek and his people with the edge of the sword. 14And the LORD said to Moses, Write this for a memorial in a book, and rehearse it in the ears of Joshua: for I will utterly blot out the remembrance of Amalek from under heaven.