Exodus 17:14-16

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.”

15And Moses built an altar and called its name, The-Lord-Is-My-Banner;

16for he said, “Because the Lord has sworn: the Lord will have war with Amalek from generation to generation.”