His sister or half-sister (and possibly step-sister of no biological relation brought up as the daughter of his biological parent) An Israelite man was not to marry or have sex with the following people: The law lists relationships, whether involving marriage or not, that God defined as incestuous.
In that passage, the Israelites are commanded not to commit incest, which is a defiling sin (Leviticus 18:24). The relationships that God forbade in the Old Testament Law are listed in Leviticus chapter 18, verses 6–18.