Exodus 17:12-16

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

And Joshua discomfited Amalek and his people with the edge of the sword.

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 Jehovah-nissi:

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