Exodus 17:8-16 - Battle With The Amalekites
8 Then Amalek came and fought with Israel in Rephidim. 9 Moses said to Joshua, "Choose men for us, and go out, fight with Amalek. Tomorrow I will stand on the top of the hill with God's rod in my hand."
10 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. 11 It happened, when Moses held up his hand, that Israel prevailed; and when he let down his hand, Amalek prevailed. 12 But Moses' hands were heavy; and 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. 13 Joshua defeated Amalek and his people with the edge of the sword.
14 Yahweh 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."