Exodus 17:10-12

10Joshua did as Moses 1told him, 2and fought against Amalek; and Moses, Aaron, and 3Hur went up to the top of the hill.

11So it came about when Moses held his hand up, that Israel prevailed, and when he let his hand 4down, Amalek prevailed.

12But Moses’ hands were heavy. Then they took a stone and put it under him, and he sat on it; and Aaron and Hur 5supported his hands, one on one side and one on the other. Thus his hands were steady until the sun set.