Genesis 26

Isaac is a patriarch who had no second wife, nor any concubine, but was content with the twins who were the fruit of a single intercourse. He too had the same fears as his father of the perilous beauty of his wife when he lived among strangers, and he too called her sister without a word about her being his wife, since in fact she was nearly related on the paternal and the maternal side. And Rebekah too was safe, once it was known that she was his wife. Not, however, that we should esteem him higher than his father for knowing no woman other than his single wife; undoubtedly the merits of his father's faith and obedience were so much greater that it was because of the father that God was so good to the son.