Naruto episode 7

"The Assassin of the Mist!"
"Kiri no ansatsusha!" (霧の暗殺者!)

After the attack, Tazuna admits that the mission is much more dangerous than originally intended, but after Team 7 hears of Tazuna's desire to build a bridge to save the impoverished Land of Waves and the threat from the wealthy criminal mastermind Gato, they agree to go through with the mission regardless for humanitarian reasons. The group is soon stopped by Zabuza Momochi, an opponent dangerous enough for Kakashi to reveal his Sharingan eye.