Naruto - Season 1 Episode 19 -

Zabuza is no longer Kakashi's enemy, and thanks to a little speech by Naruto about how ninja are, Zabuza takes on Gato's men single handedly. The Demon of the Hidden Mist takes his vengeance on Gato and all of those dumb enough to follow him, and apologizes to Haku for what he did to the kind little boy. After the group takes care of the rest of Gato's men, Zabuza asks Kakashi one final request, to see Haku one final time. This is Zabuza's requiem.