Deuteronomy 25:17-19

The Amalekites

17 Remember what the Amalekites did to you when you came out of Egypt. 18 They attacked you when you were tired and weak. They killed all the people who were walking slowly at the back of your group. They were not afraid of God. 19 But the Lord your God will chase away all your enemies. He will give you a safe place to rest in the land that he is giving to you as your new home. When he does that, do not forget to destroy all the Amalekites. Make sure that nobody in the whole world will remember them any more.

25:17The Amalekites attacked the Israelites at Rephidim. See Exodus 17:8-16.