Exodus 17:10

17:10 So Joshua fought against Amalek just as Moses had instructed him;and Moses and Aaron and Hur went up to the top of the hill.

Exodus 17:12

17:12 When the hands of Moses became heavy, they took a stone and put it under him, and Aaron and Hur held up his hands, one on one side and one on the other, and so his hands were steady until the sun went down.