Parashas Acharei Mos · Passuk 18:07
Chabad.org — English translation + Rashi
Torah Temima points to Sanhedrin 54a.
English: “Your father’s nakedness” — literally one’s father; although already derived from “you shall not lie with a male,” this verse adds a second liability.
Double liability for father
Relations with one’s father incur two distinct counts of prohibition.