Exodus 17:13 WEB

¹¹  It happened, when Moses held up his hand, that Israel prevailed; and when he let down his hand, Amalek prevailed.

¹²  But Moses' hands were heavy; and they took a stone, and put it under him, and he sat on it. Aaron and Hur held up his hands, the one on the one side, and the other on the other side. His hands were steady until sunset.

¹³  Joshua defeated Amalek and his people with the edge of the sword.

¹⁴  Yahweh said to Moses, 'Write this for a memorial in a book, and rehearse it in the ears of Joshua: that I will utterly blot out the memory of Amalek from under the sky.'

¹⁵  Moses built an altar, and called the name of it Yahweh our Banner.{Hebrew, Yahweh Nissi}