Deuteronomy 25:17-19

Deuteronomy 25:17. AMALEK TO BE EXTERMINATED.

At the end of all the precepts of humanity, the extermination of that people which is presented to us as the incarnation of inhumanity is decreed.
(18) He... smote the hindmost... — These details are not given in Exodus 17. Amalek’s attack follows the appearance of the stream of water from Horeb. There was nothing more natural than that the faint and weary should stay behind at the water side. There the Amalekites appear to have found them and cruelly massacred them.

(19) Thou shalt blot out the remembrance of Amalek. — This decree was entrusted to Joshua in the first instance, as the “servant of the Book” (Exodus 17:14); here it is enjoined upon the nation of Israel. It was carried out in several stages: by Barak and Gideon (Judges 5:14; Judges 6:3; Judges 7:12, &c.), by Saul and Samuel (1 Samuel 15), by David (1 Samuel 27:8; 1 Samuel 30:17), by the Simeonites (1 Chronicles 4:42), and lastly by Esther, who exterminated the Agagites in Haman’s house. No doubt any remnant of Amalek in the Persian empire under Mordecai would have shared Haman’s fate.