בראשית לט:ח פירוש: רמב״ן, העמק דבר, רד״ק וטור הארוך

BUT HE REFUSED, AND SAID UNTO HIS MASTER’s WIFE. Scripture relates that he refused to do her will even though she was his mistress, i.e., his master’s wife, and he feared her, for he feared G-d more. This is the meaning of the expression, unto his master’s wife.

But he refused. The verse testifies that he, without any reasoning, refused to turn his cohabitation into fornication, but that he was forced to give his master's wife ulterior reasons apart from this.

וימאן, the meaning is clear beyond mistake.