Exodus 17:13

11When Moses held up his hand, Israel prevailed. When he let down his hand, Amalek prevailed.

12But Moses’ hands were heavy; so they took a stone, and put it under him, and he sat on it. Aaron and Hur held up his hands, the one on the one side, and the other on the other side. His hands were steady until sunset.

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

14The LORD said to Moses, “Write this for a memorial in a book, and rehearse it in the ears of Joshua: that I will utterly blot out the memory of Amalek from under the sky.”

15Moses built an altar, and called its name “The LORD our Banner”.