Naruto Episode 17
Kakashi senses that Naruto has released the demon fox’s chakra, and decides he to end the fight quickly. With his new power, Naruto overwhelms Haku. Haku’s mask breaks away, revealing the boy Naruto had previously conversed with. Haku asks Naruto to kill him, as he cannot be of any more use to Zabuza. Meanwhile, Kakashi summons a number of dogs to find and restrain Zabuza. With Zabuza immobilized, Kakashi prepares his Lightning Blade.
Source: Wikipedia
Naruto Episode 17 – White Past: Hidden Ambition
