Exodus 17:13-16 New Revised Standard Version (NRSV)
13 And Joshua defeated Amalek and his people with the sword.
14 Then the Lord said to Moses, “Write this as a reminder in a book and recite it in the hearing of Joshua: I will utterly blot out the remembrance of Amalek from under heaven.” 15 And Moses built an altar and called it, The Lord is my banner. 16 He said, “A hand upon the banner of the Lord![a] The Lord will have war with Amalek from generation to generation.”