Season 5 Episode 2 - Redux II (3) 

Cigarette Smoking Man helps Mulder to obtain Scully's cure and also lets him see his real sister who doesn't turn out to be as happy to see Mulder as he would've liked. In return for this, CSM asks that Mulder quit the FBI and work for him.
Keywords: x-files, scully, mulder, full episode, season 5, episode 2, redux ii (3), 5x02