Exodus 17:9 KJV

7And he called the name of the place Massah, and Meribah, because of the chiding of the children of Israel, and because they tempted the LORD, saying, Is the LORD among us, or not?

8Then came Amalek, and fought with Israel in Rephidim.

9And Moses said unto Joshua, Choose us out men, and go out, fight with Amalek: to morrow I will stand on the top of the hill with the rod of God in mine hand.

10So Joshua did as Moses had said to him, and fought with Amalek: and Moses, Aaron, and Hur went up to the top of the hill.

11And it came to pass, when Moses held up his hand, that Israel prevailed: and when he let down his hand, Amalek prevailed.