Exodus 17:14-16

And the LORD said unto Moses, Write this for a memorial in a book, and rehearse it in the ears of Joshua: for I will utterly put out the remembrance of Amalek from under heaven.

And Moses built an altar, and called the name of it Jehovahnissi:

For he said, Because the LORD hath sworn that the LORD will have war with Amalek from generation to generation.