Parashas Acharei Mos · Passuk 18:29
Chabad.org — English translation + Rashi
Torah Temima points to Kiddushin 67b.
English: From where that kiddushin does not take effect with arayot? They are compared to a wife’s sister: just as kiddushin does not take effect with her, so with all the arayot.
No kiddushin with arayot
A betrothal or marriage bond cannot be created with a partner from the list of forbidden relations.