Genesis 28:9

then went Esau unto Ishmael, that is, to the house of Ishmael, the father himself having been dead more than twelve years, and took unto, in addition to, the wives which he had Mahalath, the daughter of Ishmael, Abraham's son, the sister of Nebajoth, to be his wife. This woman, Genesis 36:2, is called Bashemath, and she was called the sister of Nebajoth, because he was her oldest brother. Esau probably intended to regain the full regard of his father by this act, since this third wife was a descendant of Abraham, but merely betrayed his utter lack of understanding, so far as the relation of the patriarchs to the prophecies of the Lord with regard to the possession of this land was concerned, for Ishmael and his children were not to be heirs with the son of Sarah.