If a man marries his sister, whether the daughter of his father or of his mother, and they have sexual relations, it is a disgrace. They must be cut off in the sight of their people. He has uncovered the nakedness of his sister; he shall bear his iniquity.
Jewish Publication Society of America Version (JPS1917) - Leviticus 20:17 >And if a man shall take his sister, his father's daughter, or his mother's daughter, and see her nakedness, and she see his nakedness: it is a shameful thing; and they shall be cut off in the sight of the children of their people: he hath uncovered his sister's nakedness; he shall bear his iniquity.