This Bible contradiction is from the Skeptic's Annotated Bible.

Verses

Incestuous marriage condemned.

Leviticus 18:9 View context

The nakedness of thy sister, the daughter of thy father, or daughter of thy mother, [whether she be] born at home, or born abroad, [even] their nakedness thou shalt not uncover.

Leviticus 20:17 View context

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 wicked thing; and they shall be cut off in the sight of their people: he hath uncovered his sister's nakedness; he shall bear his iniquity.

Deuteronomy 27:22 View context

Cursed [be] he that lieth with his sister, the daughter of his father, or the daughter of his mother. And all the people shall say, Amen.

Incestuous marriage approved.

Genesis 20:12 View context

And yet indeed [she is] my sister; she [is] the daughter of my father, but not the daughter of my mother; and she became my wife.

Genesis 17:16 View context

And I will bless her, and give thee a son also of her: yea, I will bless her, and she shall be [a mother] of nations; kings of people shall be of her.

Exodus 6:20 View context

And Amram took him Jochebed his father's sister to wife; and she bare him Aaron and Moses: and the years of the life of Amram [were] an hundred and thirty and seven years.