The Consequences of Betrayal

is episode 45 of the Naruto: Shippūden anime.

Synopsis
To confuse and therefore slow down Yamato's wood clone, Kabuto modifies a corpse to resemble Sai. During their pursuit to find Sai, the team is forced to take a break when Sakura's own injuries takes their toll on her. Yamato takes Naruto to one side and tells him that it was he, in his Four-Tailed form, who hurt Sakura. Naruto is shocked to discover this, and condemns his own actions, vowing to never use the fox's power again in order to not hurt those he cares for again.