Leviticus 18:7

אביך‎ ערות‎ THE NAKEDNESS OF THY FATHER, [AND THE NAKEDNESS OF THY MOTHER SHALT THOU NOT UNCOVER] — This refers to intercourse with thy father's wife (no matter whether she is thy own mother or thy stepmother). Or perhaps this is not so, but ערות אביך has to be taken literally (as sodomy)?! Scripture, however, uses the expression ערות אביך here, and it is said later on (Leviticus 20:11) “And the man that lieth with his father's wife hath uncovered his father's nakedness (״(ערות אביו גלה. Now what is the meaning of ערות אביו there? It refers to one's fathers wife! so does ערות אביך here also refer to one's father's wife (Sanhedrin 54a). וערות אמך AND THE NAKEDNESS OF THY MOTHER [SHALT THOU NOT UNCOVER] — This is intended to include in the prohibition the marriage of one's own mother although she be not the wife of one's father (Sanhedrin 54a).

עֶרְוַ֥ת אָבִ֛יךָ וְעֶרְוַ֥ת אִמְּךָ֖ לֹ֣א תְגַלֵּ֑ה אִמְּךָ֣ הִ֔וא לֹ֥א תְגַלֶּ֖ה עֶרְוָתָֽהּ׃ {ס}        

The nakedness of thy father, or the nakedness of thy mother, shalt thou not uncover: she is thy mother; thou shalt not uncover her nakedness.