Shemot 17:9-11

Orthodox Jewish Bible

⁹ And Moshe said unto Yehoshua, Choose for us anashim, and go out, do battle with Amalek; tomorrow I will station myself on the top of the hill with the matteh HaElohim in mine yad.

¹⁰ So Yehoshua did as Moshe had said to him, and did battle with Amalek; and Moshe, Aharon, and Chur went up to the top of the hill.

¹¹ And it came to pass, as long as Moshe held up his yad, that Yisroel prevailed; and when he let down his yad, Amalek prevailed.