Exodus 17:14-16

and Jehovah said unto Moses, Write this for a memorial in a book, and rehearse it in the ears of Joshua: that I will utterly blot out the remembrance of Amalek from under heaven. And Moses built an altar, and called the name of it Jehovah-nissi; and he said, Jehovah hath sworn: Jehovah will have war with Amalek from generation to generation.