Midrasch zu Bereschit 36:24

You find likewise (that the expression sat also alludes to) the degeneracy of the descendants of Seir, since it is written: These are the sons of Seir the Horite, who sat on the land: Lotan and Shobal and Zibeon and Anah (Gen. 36:20). However, Anah is elsewhere called the son of Zibeon: And these are the children of Zibeon: Aiah and Anah (ibid., v. 24). We learn from this that Zibeon had sexual relations with his own mother, and conceived and begot Anah by her. Consequently, (Anah) was both (Zibeon’s) brother and his son. Later he had intercourse with his daughter-in-law, the wife of Anah, and Oholibamah was their child, as it is said: And these were the sons of Oholibamah the daughter of Anah, the daughter of Zibeon, Esau’s wife (ibid., v. 14), and Esau took her as a wife. Inasmuch as they were all products of incestuous relations, Scripture mentions them only to disclose their degeneracy.