it’s written in the torah that reuben lay down with bilhah and that his father jacob heard about it. (genesis 35:22) though the talmud says that this was a metaphor and that reuben actually took bilhah’s bed from his father’s tent but that this was seen as being like the sin of incest (shabbat 55) and says that this works because in the book of job wanting to commit incest is seen as committing incest.