Exodus 17:12-15

But Moses’ hands were heavy. Then they took a stone and put it under him, and he sat on it; and Aaron and Hur supported his hands, one on one side and one on the other. Thus his hands were steady until the sun set. So Joshua overwhelmed Amalek and his people with the edge of the sword. Then the LORD said to Moses, “Write this in a book as a memorial and recite it to Joshua, that I will utterly blot out the memory of Amalek from under heaven.” Moses built an altar and named it The LORD is My Banner