Midrash su Genesi 39:8

But he refused, and said unto his master’s wife (Gen. 39:8). Scripture states elsewhere in reference to this verse: Blessed is the man that trusteth in the Lord (Jer. 17:7). You find that while Joseph dwelt in his master’s home, the Lord was with Joseph, and he prospered, and his master saw that the Lord was with him (Gen. 39:2–3). How did the wicked Potiphar recognize, then, that the Holy One, blessed be He, was with him? In what way was the Lord with him? The name of the Holy One, blessed be He, never left Joseph’s lips. When Joseph entered to serve him, he would whisper to himself: “Master of the Universe, you are the One in whom I trust; you are the One who is my protector, may I find grace, kindness, and mercy in your sight, and in the sight of all who see me, and in the eyes of my master, Potiphar.” Thereupon Potiphar asked him: “What are you whispering about? Perhaps you are trying to weave a spell over me?” “No,” he replied, “I am praying that I may find favor in your sight.” Hence it is written: And his master saw that the Lord was with him.

And he did not listen to her to lie down with her - in this world. 'To be with her' in Gehena, in the world to come. And another opinion: 'He did not listen to her' he did not even touch her bed. A certain Roman Matron asked Rabbi Yosi: Is it really possible that Yosef, a young man of 17 resisted all his heat and did this? Rabbi Yosi took out the book of Bereshit and began reading for her the stories of Reuven and Bilhah, Yehudah and Tamar, and said: 'if with those, adults and under their father's authority the Scripture did not hide their misdeed, with this one, not an adult and by himself, all the more so it would have revealed the misdeed!