343. Rabbi Aba was going to Cappadocia with Rabbi Yosi. As they were going, they saw a man approaching there who had a mark on his face. Rabbi Aba said: Let us leave this road as this man's face testifies that he transgressed the rules of incest in the Torah. Therefore, his face is marked. Rabbi Yosi replied: If he had this mark since childhood, what incest would be then with him? He replied: I see his face testifying that he transgressed on a sexual misconduct mentioned in the Torah.
393. "You shall not uncover the nakedness of mother and daughter" (Vayikra 18:17). We have learned that these kinds of incest are among the laws of the Queen, even though they are both revealed and hidden. There are listed "her son's daughter, or her daughter's daughter" (Ibid.), for the world needs them to populate the world, as we have learned. One who reveals one nakedness of these, woe to him and woe to his soul, as because of this he will uncover other nakednesses.