Daily Mitzvot

Do not be sexually intimate with one’s sister, whether from only the same father or only the same mother, even from an immoral relationship

 

 “You shall not uncover the nakedness of your sister, the daughter of your father or daughter of your mother, whether born at home or abroad” Vayikra 18:9

If done wilfully the penalty is spiritual severance,

If unwittingly a sin offering is required.

If she is also the daughter of his father’s wife one would be obligated to bring 2 sin offerings.   (Includes -128)

 

This applies in all places at all times