민수기 31:7의 Parshanut

They mounted a campaign. In the Sefer HaMitzvos, Ramban counts this as a positive commandment. In the Sifei, the Sages derived that the enemy should not be surrounded on four sides from, “as Adonoy had commanded Moshe.” Ramban held the view that just as it is a commandment to seek peace, so too, it is a commandment to leave them a side to flee so they can save their lives. Rambam, however, does not count this as a positive commandment, because he held the view that this is a strategy of warfare. If Bnei Yisroel were to surround their enemy on all sides, this would cause them to despair that they will fall captive to their enemy, and they will be fortified with all their strength to fight valiantly. Therefore, this was not relevant to be counted as a positive commandment.