Genesis 26:34
And Esau was forty years old when he took to wife Judith the daughter of Beeri the Hittite, and Bashemath the daughter of Elon the Hittite: And Esau was forty years old when he took to wife Judith the daughter of Beeri the Hittite, and Bashemath the daughter of Elon the Hittite:
Esau was forty years old when he took to wife Judith the daughter of Beeri the Hittite and Bashemath the daughter of Elon the Hittite. Both wives were Hittites from among the idolatrous Canaanites, women who worshiped false gods. Their marriages were a grief to Isaac and Rebekah, a great grief and bitter grief of mind to them.
In taking them Esau violated the command given to his forefathers not to marry idolaters, the covenant prohibition against intermarriage between God's chosen people and the heathen. His course stood in contrast to Abraham's careful choice of a wife of his own nation and faith for Isaac. Despite the grief they caused, Isaac continued to love Esau better and more than Jacob, and when he thought he was about to die he asked Esau to prepare savory meat for him so that he could bless him before his death.
Esau had lightly regarded his birthright, had sold it to Jacob and confirmed the sale with an oath, yet he did not tell Isaac about the sale.