Deuteronomy 25:17-19

17Remember what Amalek did to thee by the way, when ye had come forth from Egypt; 18How he met thee by the way, and smote those behind thee, even all that were feeble behind thee, when thou wast faint and weary; and he feared not God. 19Therefore it shall be, when the LORD thy God hath given thee rest from all thy enemies on all sides, in the land which the LORD thy God giveth thee for an inheritance to possess it, that thou shalt blot out the remembrance of Amalek from under heaven; thou shalt not forget it .