Exodus 17:11-14

11And so it was, when Moses held up his hand, that Israel prevailed; and when he let down his hand, Amalek prevailed.

12But Moses’ hands became heavy; so they took a stone and put it under him, and he sat on it. And Aaron and Hur supported his hands, one on one side, and the other on the other side; and his hands were steady until the going down of the sun.

13So Joshua defeated Amalek and his people with the edge of the sword.

14Then the Lord said to Moses, “Write this for a memorial in the book and recount it in the hearing of Joshua, that I will utterly blot out the remembrance of Amalek from under heaven.”