Genesis 25:19-22

And these are the generations of Isaac, Abraham's son: Abraham begat Isaac: and Isaac was forty years old when he took Rebekah to wife, the daughter of Bethuel the Syrian of Padan-aram, the sister to Laban the Syrian. And Isaac intreated the LORD for his wife, because she was barren: and the LORD was intreated of him, and Rebekah his wife conceived. And the children struggled together within her; and she said, If it be so, why am I thus? And she went to enquire of the LORD.