Exodus 17:8-13 Commentary
When Moses held up his hand, Israel prevailed; and when he let down his hand, Amalek prevailed. 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. Joshua defeated Amalek and his people with the edge of the sword.