A Shinobi's Determination

is episode 90 of the Naruto: Shippūden anime.

Synopsis
An ANBU sends a message to Konoha moments before he dies, having discovered what may be Orochimaru's current hideout. Meanwhile, Orochimaru has Guren initiate a battle among a large number of experimental specimens with the survivors being used for a future operation. Naruto is warned not to use Rasenshuriken due to its extreme risk, and Sasuke meets a boy called Yūkimaru. Kakashi is ordered to go on a reconnaissance mission with Shino, Kiba and Hinata. Naruto is reunited with Jiraiya, who offers to train with him again.

Trivia

 * There's a slight possibility that place where Sasuke was training near the waterfall, is the same waterfall where Sasuke trained at the beginning of Naruto Shippūden 2: Bonds Movie.