Deuteronomy 27:22

Blessings And Curses

²¹ Cursed is the one who commits bestiality.' Then all the people will say, 'Amen!' ²² Cursed is the one who has sexual relations with his sister, the daughter of either his father or mother.' Then all the people will say, 'Amen!' ²³ Cursed is the one who has sexual relations with his mother-in-law.' Then all the people will say, 'Amen!'

Sexual Relations

Leviticus 18:9

You must not have sexual intercourse with your sister, whether she is your father's daughter or your mother's daughter, whether she is born in the same household or born outside it; you must not have sexual intercourse with either of them.

Leviticus 20:17

"'If a man has sexual intercourse with his sister, whether the daughter of his father or his mother, so that he sees her nakedness and she sees his nakedness, it is a disgrace. They must be cut off in the sight of the children of their people. He has exposed his sister's nakedness; he will bear his punishment for iniquity.

Ezekiel 22:11

One commits an abominable act with his neighbor's wife; another obscenely defiles his daughter-in-law; another violates his sister -- his father's daughter -- within you.

2 Samuel 13:1

Now David's son Absalom had a beautiful sister named Tamar. In the course of time David's son Amnon fell madly in love with her.

2 Samuel 13:8-14

So Tamar went to the house of Amnon her brother, who was lying down. She took the dough, kneaded it, made some cakes while he watched, and baked them.