TT #319 · Parashas Shoftim · Seventh Aliyah · Passuk 20:16
Only from the cities of these peoples that the Eternal your God is giving you as an inheritance, you shall not leave alive any soul.
Torah Temimah points to Sifrei Devarim 200 / Sotah.
TT lemma: לֹא תְחַיֶּה כׇּל נְשָׁמָה.
Sefaria — Sifrei Devarim 200 / Sotah
English: ‘You shall not leave alive any soul’ – a positive commandment.
Derash classifying the command (Sifrei) — the language creates a positive duty of herem.
Regarding the cities of the seven nations in the Land, the Torah commands that no soul be left alive.