Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 49
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 49, with English translation by Maimonides (Rambam).
שלא להחיות אדם משבעה עממים, שנאמר "לא תחייה, כל נשמה" (דברים כ,טז).
Not to allow a single member of the seven [Canaanite] nations to live, as [Deuteronomy 20:16] states: "Do not allow a soul to live."