Charles Ellicott Commentary Genesis 26:7

"And the men of the place asked him of his wife. And he said, She is my sister. For he feared to say, My wife. Lest, [said he], the men of the place should kill me for Rebekah. Because she was fair to look upon." — Genesis 26:7 (ASV)

He said, She is my sister. —We have already seen that Abraham at Gerar showed no awareness of having done wrong in denying his wife (Genesis 20:2); and we now find Isaac imitating his example with even less reason for his conduct.

The circumstances are, however, different. It is the people who inquire about Isaac’s relation to Rebekah, and though she was fair to look upon, yet no annoyance followed his denial of her. The king after a long time detects their intimacy; but there are no presents, and no marks of respect to Rebekah, and no friendship. It is only after long quarrels, during which Isaac is obliged to withdraw to a long distance from Gerar, that finally peace is made between them.