By Rabbi Pinchas Hackenbroch, November 25, 2010
Joseph, resisting the advances of his master Potiphar's wife, says that it was improper for him on two counts: firstly, because of the debt of gratitude that he owed Potiphar and, secondly, because it would be a terrible sin against God to commit adultery.
Rav Mordechai Gifter (1915-2001) raises an interesting question. Why, when repelling Potiphar wife's advances, did he not state why it was wrong and inappropriate for her, rather than him, to commit such an act? Rashi quotes a talmudic statement that even before the Torah was given, non-Jews were commanded against immorality.