Naruto Shippūden - Season 4 Episode 76

Kakashi reveals that while he knows how to perform Rasengan, he cannot combine his own lightning-based chakra. He adds that even the Fourth Hokage, who created the move, could not combine his elemental chakra with the technique, but that Naruto might be able to. Asuma sends word to other teams about Akatsuki’s location and proceeds on despite his concern about Akatsuki’s strength. Kakuzu turns in Chiriku’s corpse despite Hidan’s complaints, and says that he is partnered with Hidan because he cannot kill him. The stress of the training causes Naruto to be enveloped in the Nine-tails's "Demon Fox's Cloak", but Yamato suppresses it.