Gênesis 26
Augustine of Hippo · Comentário Patrístico (catena)
Gênesis 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. — City of God 16.36
Gênesis 26:7
Those who assert that sometimes we must lie make inappropriate mention of Abraham as having lied about Sarah whom he called his sister. For he did not say "She is not my wife" but "She is my sister," because Sarah was in fact of a family so closely related that without lying she could be called his sister. This fact Abraham confirmed afterward when Sarah was returned by him who had led her away. Abraham replied to him, saying, "Also she is truly my sister, the daughter of my father, and not the daughter of my mother," that is to say, belonging to his father's family but not to his mother's. Thus he concealed something of the truth but did not say anything false in concealing the fact that she was his wife and in saying that she was his sister. His son Isaac also did this, for we know that he too chose a relative of his as wife. Hence it is not a lie when truth is passed over in silence but when falsehood is brought forth in speech. — Against Lying 10.23