S1·E9 The Engagement Ring

Barney decides to surprise Betty with a belated engagement ring, which he gives to Fred for safekeeping. But Wilma discovers the ring and assumes it is a gift for her. Not wanting to shatter her illusions, Fred decides to buy a second ring, but doesn't have the cash. He cons Barney into going several rounds with a boxing champ in order to win a $500 prize.