Genesis 26:5

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.

But what is the meaning of "for the reason that he obeyed my voice and kept my commands, my orders, and my judgments"? I said to Abraham, "Go forth from your country and your kindred, onward to a land that I will show you." He left what he had and set off for an uncertain goal. He did not dally or delay; instead, with complete enthusiasm, Abraham obeyed my call and carried out my commands. In turn I promised him things beyond nature and, despite his despair on the score of age and the unsuitability for childbearing on the part of himself and your mother, he heard from me that his descendants would develop into such a great number as to fill the whole land. Yet he did not become deranged in mind or lose faith. Hence it was reckoned as righteousness in Abraham to trust in my power and have confidence in my promises.…After your birth your mother was ill disposed toward her maidservant's child Ishmael and wanted to drive him out of the house with Hagar so that he should have nothing in common with you. The patriarch had some natural inclination toward him out of his fatherly affection; but when he heard from me, "Do what Sarah wants," he ignored his natural affection and drove out Ishmael along with the maidservant, obeying my call and keeping my commands in every detail. I mean, when he received the ultimate command from me to offer up as a sacrifice the son he so much desired, the gift of his old age, Abraham did not pry into the reasons. Neither was he disturbed in his thinking; nor did he betray the news to your mother or reveal to you what was about to be done by him. Instead, with steadfast resolve and heightened zeal, he pressed ahead to put my command into effect. So I rewarded his intention by preventing the execution of the deed. Since, then, he had in everything given evidence of complete obedience and observance of my commands, consequently I am making you, his child, the inheritor of the promises made to him. So imitate his obedience, and believe my words so as to be found worthy of a manifold reward for your father's virtue and also for your own obedience. Don't go down into Egypt; rather, stay here. Do you see God's loving kindness in strengthening Isaac's resolve through the memory of his father's virtue?