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 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.

Cross-references

Leviticus 18:9 forbids relations with a sister — the act this verse punishes with being cut off.

Leviticus 18:6 gives the general prohibition of uncovering close relatives' nakedness, which this verse applies specifically to a sister.

Genesis 20:12 shows Abraham married his half-sister — a relationship later prohibited and penalized here.

Deuteronomy 27:22 pronounces a curse on lying with a sister — reinforcing the same prohibition.

In 2 Samuel 13:12, Tamar calls incest 'not done in Israel' — directly reflecting this law's standard.