Top and skirt worn by Cobie Smulders in episode seven of season four "Not a Father's Day", when Ted is talking about how Robin reacted when she met his cousin and her daughter.
The skirt was used again in episode nine of season four "The Naked Man", when Ted is telling his children some of the incidents he has walked in on in the apartment, you see the time when he walked in on Barney performing a trick were he is in a tank full of water trying to free himself from his restraints, Marshall is timing Barney and Lily and Robin are on either side of the tank with axes ready to smash it if Barney can't get free.
I don't think that the wardrobe tag that comes with the outfit is the correct tag.
