A New Formation: Ino–Shika–Chō!

is episode 145 of the original Naruto anime.

Synopsis
Team 10 tells Naruto that they will take care of the brothers, and use their combined skills to immobilize them. Naruto leaves to catch up to Iruka, who is fighting Mizuki in a building used to test Ninja Academy instructors. It is revealed that Iruka and Mizuki are childhood friends, although Mizuki only hoped to get close to the Hokage. Mizuki reveals that he has become stronger and learned new techniques while in prison, and destroys the building they are in.