Rashi on Genesis 34:7/רש"י על בראשית ל״ד:ז׳

1וכן לא יעשה AND THUS IT OUGHT NOT TO BE DONE — viz., to do violence to a maiden, for even the heathens have trained themselves (literally, have fenced themselves round) against unchastity as a consequence of the Flood which had come upon the world as a punishment for this sin (Genesis Rabbah 80:6).