Leviticus 18:1-3, 6, 9

Then the LORD said to Moses, “Give the following instructions to the people of Israel. I am the LORD your God. So do not act like the people in Egypt, where you used to live, or like the people of Canaan, where I am taking you. You must not imitate their way of life.

“You must never have sexual relations with a close relative, for I am the LORD.

“Do not have sexual relations with your sister or half sister, whether she is your father’s daughter or your mother’s daughter, whether she was born into your household or someone else’s.