Leviticus 20:17-18

17It is a sin if a man marries his sister. She may be the daughter of his father or of his mother. It is a sin if he has sex with her. The people must send them away. He has taken away his sister's honour. He must carry the punishment for his sin.

18A man must not have sex with a woman when she is bleeding. If he does, it is a sin. They have not obeyed the rules of the Lord. The people must send them away.