Exodus 17:11

Then Amalek came and fought with Israel in Rephidim.

Moses said to Joshua, “Choose men for us, and go out to fight with Amalek. Tomorrow I will stand on the top of the hill with God’s rod in my hand.”

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

But Moses’ hands were heavy; so they took a stone, and put it under him, and he sat on it. Aaron and Hur held up his hands, the one on the one side, and the other on the other side. His hands were steady until sunset.

Joshua defeated Amalek and his people with the edge of the sword.

The LORD said to Moses, “Write this for a memorial in a book, and rehearse it in the ears of Joshua: that I will utterly blot out the memory of Amalek from under the sky.”