The 338th prohibition is that one is forbidden from having relations with a woman and her son's daughter.
The source of this commandment is G‑d's statement,1 "[do not commit incest with a woman and her daughter.] Do not even take her son's daughter."
For this prohibition, too, the punishment is s'reifah and kares for an intentional transgression, and a sin-offering if unintentional.
