You shall destroy all the peoples that the ETERNAL your God delivers to you, showing them no pity. And you shall not worship their gods, for that would be a snare to you.
ואכלת וגו'. אמר רב הונא, מניין לגזל עובד כוכבים שהוא אסור, שנאמר ואכלת את כל העמים אשר ה' אלהיך נותן לך, בזמן שהם מסורים בידך ולא בזמן שאין מסורים בידך
English: Rav Huna said: Whence that robbery of a non-Jew is forbidden? As it is said, “You shall consume all the peoples that Hashem your God gives you” — when they are delivered into your hand, and not when they are not delivered into your hand.
On the daf / in context: Bava Kama 113b; cf. Behar on fair dealing.
Type of Learning
Custom (halakhic inference — gezel akum)
What Is Learned
Taking from the nations is permitted only when they are delivered in war; peacetime robbery of a non-Jew remains forbidden.