Exodus 17:10; Exodus 17:12

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

12 But 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 one side and one on the other. Thus his hands were steady until the sun set.