Exodus 17:15

10 So Joshua did as Moses said to him, and went to war with Amalek: and Moses, Aaron, and Hur went up to the top of the hill.

11 Now while Moses' hand was lifted up, Israel was the stronger: but when he let his hand go down, Amalek became the stronger.

12 But Moses' hands became tired; so they put a stone under him and he took his seat on it, Aaron and Hur supporting his hands, one on one side and one on the other; so his hands were kept up without falling till the sun went down.

13 And Joshua overcame Amalek and his people with the sword.

14 And the Lord said to Moses, Make a record of this in a book, so that it may be kept in memory, and say it again in the ears of Joshua: that all memory of Amalek is to be completely uprooted from the earth.

15 Then Moses put up an altar and gave it the name of Yahweh-nissi:

16 For he said, The Lord has taken his oath that there will be war with Amalek from generation to generation.