Leviticus 18:1-3, 6, 9

Then the LORD spoke to Moses, saying, “Speak to the children of Israel, and say to them: ‘I am the LORD your God. According to the doings of the land of Egypt, where you dwelt, you shall not do; and according to the doings of the land of Canaan, where I am bringing you, you shall not do; nor shall you walk in their ordinances.

‘None of you shall approach anyone who is near of kin to him, to uncover his nakedness: I am the LORD.

The nakedness of your sister, the daughter of your father, or the daughter of your mother, whether born at home or elsewhere, their nakedness you shall not uncover.