Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 188
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 188, with English translation by Maimonides (Rambam).
להכרית זרעו של עמלק, שנאמר: "תמחה את זכר עמלק" (דברים כה,יט).
To exterminate the seed of Amalek, as [Deuteronomy 25:19] states: "Blot out the memory of Amalek."