Naruto Season 2 Episode 91
Inheritance! The Necklace of Death!
Naruto makes a bet with Tsunade, that if he can master the Rasengan in one week, she'll give him a necklace belonging the to the First Hokage. However, Shizune reveals some startling information. Everybody, except for Tsunade, who's worn that necklace has died the next day!