Exodus 17:16 KJV
For he said, Because the Lord hath sworn that the Lord will have war with Amalek from generation to generation.
Exodus 17:16, King James Version
In context
15 And Moses built an altar, and called the name of it JEHOVAH–nissi:
16 For he said, Because the Lord hath sworn that the Lord will have war with Amalek from generation to generation.