Leviticus 18:9-11

9“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.

10“Do not have sexual relations with your granddaughter, whether she is your son’s daughter or your daughter’s daughter, for this would violate yourself.

11“Do not have sexual relations with your stepsister, the daughter of any of your father’s wives, for she is your sister.