Exodus 17:12-15

Moses’ arms soon became so tired he could no longer hold them up. So Aaron and Hur found a stone for him to sit on. Then they stood on each side of Moses, holding up his hands. So his hands held steady until sunset. As a result, Joshua overwhelmed the army of Amalek in battle. After the victory, the LORD instructed Moses, “Write this down on a scroll as a permanent reminder, and read it aloud to Joshua: I will erase the memory of Amalek from under heaven.” Moses built an altar there and named it Yahweh-Nissi (which means “the LORD is my banner”).