Exodus 17:10-12

Young's Literal Translation

¹⁰ And Joshua doth as Moses hath said to him, to fight with Amalek, and Moses, Aaron, and Hur, have gone up [to] the top of the height;

¹¹ and it hath come to pass, when Moses lifteth up his hand, that Israel hath been mighty, and when he letteth his hands rest, that Amalek hath been mighty.

¹² And the hands of Moses [are] heavy, and they take a stone, and set [it] under him, and he sitteth on it: and Aaron and Hur have taken hold on his hands, on this side one, and on that one, and his hands are stedfast till the going in of the sun;