The Broken Seal

is episode 16 of the original Naruto anime.

Synopsis
Sasuke is holding his own against Haku, activating his Sharingan, which allows him to track Haku's incredibly fast movements. Naruto stubbornly refuses to accept that Haku is too fast for him, but he is running low on chakra and faints. Haku, realizing that Sasuke would have the advantage in a drawn out fight, targets the vulnerable Naruto with a volley of senbon, and Sasuke instinctively moves to defend his teammate. Naruto wakes up and sees Sasuke standing in front of him, struck by many senbon. Naruto is shocked and catches Sasuke as he collapses. Believing his teammate has died in his arms, Naruto is enraged and unconsciously taps into the chakra of the Nine-Tailed Fox within him. Haku watches in disbelief as the fox's power heals Naruto's wounds. Naruto attacks and punches Haku through the mirrors of ice dispelling the Demonic Mirroring Ice Crystals.

Trivia

 * Although edited out of Cartoon Network's airing of Sasuke and Sakura: Friends or Foes?, the scene of Naruto accidentally kissing Sasuke was shown in the flashback sequence of this episode when it aired.