Devarim 25:17-19
Remember what Amalek did to you on your journey, after you left Egypt--how, undeterred by fear of G-d, he surprised you on the march, when you were famished and weary, and cut down all the stragglers in your rear. Therefore, when Hashem your G-d grants you safety from all your enemies around you, in the land that Hashem your G-d is giving you as a hereditary portion, you shall blot out the memory of Amalek from under heaven. Do not forget!