Exodus 17:11-12 ▼

11 So it happened when Moses raised his hand up, that Israel prevailed, and when he let his hand down, Amalek prevailed.

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.