Exodus 17:10-12

10Joshua did just 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; but when he let his hand 4down, Amalek prevailed.

12And Moses’ hands were heavy. So 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. So his hands were steady until the sun set.