Naruto arrives and manages a sneak attack on Haku. Although Zabuza tries to attack Naruto, Haku asks to be the one to fight him, and Zabuza agrees. Trying to help Sasuke, Naruto enters the cage of mirrors, becoming trapped as well.
Source: Wikipedia
Naruto Episode 14 – The Number One Hyperactive, Knucklehead Ninja Joins the Fight!