Exodus 17:12-15

Later, when Moses’ arms became tired, the men put a large rock under him, and he sat on it. Then Aaron and Hur held up Moses’ hands—Aaron on one side and Hur on the other. They kept his hands steady until the sun went down. So Joshua defeated the Amalekites in this battle. Then the LORD said to Moses, “Write about this battle in a book so people will remember. And be sure to tell Joshua, because I will completely destroy the Amalekites from the earth.” Then Moses built an altar and named it The LORD Is My Banner.