Leviticus 18:9

‘If there is a man who takes his sister, his father’s daughter, or his mother’s daughter, so that he sees her nakedness and she sees his nakedness, it is a disgrace; and they shall be cut off in the sight of the sons of their people. He has uncovered his sister’s nakedness; he bears his guilt.

‘Cursed is he who lies with his sister, the daughter of his father or the daughter of his mother.’ And all the people shall say, ‘Amen.’

But he was not willing to listen to her voice. Now he was stronger than she, so he violated her and lay with her.

but that we write to them that they abstain from things contaminated by idols and from sexual immorality and from what is strangled and from blood.