Isaac tells Abimelech Rebekah is his sister
Isaac said that Rebekah was his sister. Abimelech found out the truth and warned everyone.
Key passages
Ge 26:6–11

So Isaac settled in Gerar. When the men of the place asked concerning his wife, he said, “She is my sister,” for he was afraid to say, “my wife,” thinking “the men of the place will kill me on account of Rebekah, for she was beautiful.” And it happened that, when he had been there a long …

See also
Important Things