Exodus 17:11-14

11And it came to pass when Moses raised his hand, that Israel prevailed; and when he let down his hand, Amalek prevailed.

12And 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 this side, and one on that side; and his hands were steady until the going down of the sun.

13And Joshua broke the power of Amalek and his people with the edge of the sword.

14And Jehovah said to Moses, Write this [for] a memorial in the book, and rehearse [it] in the ears of Joshua, that I will utterly blot out the remembrance of Amalek from under the heavens.