Lev Leviticus3. Mosebok, chapterkapittel Book of LeviticusTredje Mosebok, chapterkapittel 20

A man who marries his sister, whether she's his father's daughter or his mother's daughter, and they have sex, has done something shameful. They must be expelled from their people in front of everybody. He has brought shame on his sister; he bears the responsibility for his punishment.