Musannaf Ibn Abi Shayba 37:235

Hudhayfah said: "Indeed, the trial is presented to the hearts; so whichever heart absorbs it, a black dot is placed upon it. And whichever heart rejects it, a white dot is placed upon it. So whoever among you wishes to know whether the trial has afflicted him or not, let him look: if he sees a forbidden thing that he used to see as permissible, or he sees a permissible thing that he used to see as forbidden, then it has afflicted him."