Rashi on Genesis 26:34/רש"י על בראשית כ״ו:ל״ד

1בן ארבעים שנה [AND ESAU WAS] FORTY YEARS OLD —Esau is compared to a boar, as it is said, (Psalms 80:14) “The boar from the wood doth ravage it”. The boar when it lies down stretches forth its cloven hoof as much as to say, “See, I am a clean animal” (whilst really cloven hoofs are a feature of clean animals only in conjunction with another that is lacking in the swine). In the same way these dukes of Esau rob and extort and pretend to be honorable (Genesis Rabbah 65:1). For the whole forty years Esau enticed women from their husbands and ill-treated them; when he reached the age of forty he said, “My father took a wife when he was forty and I shall do the same” (Gen. R. 65).