Rashi on Deuteronomy 20:11/רש"י על דברים כ׳:י״א

1כל העם הנמצא בה ALL THE PEOPLE THAT IS FOUND THEREIN [SHALL BE TRIBUTARIES] — all: even if you find in it persons belonging to the seven nations which you have been commanded to exterminate, you are allowed to keep them alive (Sifrei Devarim 200:2).

2למס ועבדוך [ALL THE PEOPLE … SHALL BE] TRIBUTARIES [UNTO THEE], AND THEY SHALL SERVE THEE — You must not accept their surrender until they take upon themselves both the payment of tribute and servitude (one alone is not sufficient) (Sifrei Devarim 200:3).