Exodus 17:10-13

10And Joshua did as Moses had said to him, to fight with Amalek; and Moses, Aaron and Hur went up to the top of the hill.

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

12And Moses' hands were heavy; then they took a stone, and put [it] under him, and he sat on it; and Aaron and Hur supported his hands, one on this side, and one on that side; and his hands were steady until the going down of the sun.

13And Joshua broke the power of Amalek and his people with the edge of the sword.