Exodus 17:11-12

New American Standard Bible

¹¹ So it came about, when Moses held his hand up, that Israel prevailed; but when he let his hand ^[a]down, Amalek prevailed. ¹² And Moses’ hands were heavy. So they took a stone and put it under him, and he sat on it; and Aaron and Hur ^(A)supported his hands, one on one side and one on the other. So his hands were steady until the sun set.