ציטירנדיקער פּירוש אויף דברים 20:6

ושבית שביו, “and you take back some captives.” According to Rashi, this includes Canaanites that were in that land or city; [in spite of the commandment not to allow any Canaanite to survive, as per Deut. 20,6. Ed.] If you were to wonder how this could be, remember that the Torah speaks of an expansionary war, outside the borders of what used to be the Canaanite land that was promised by G–d to Avraham. If the prisoner had been captured outside those boundaries, the fact that she is now brought back to what used to be the land of Canaan does not make her subject to the commandment stated in Deut. 20,16.