"The Broken Seal" (解放された封印, Kaihō Sareta Fūin) is episode 16 of the original Naruto anime.
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, realising 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 shield 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, which both Kakashi and Zabuza sense and makes Kakashi wonder if the seal is broken. Haku watches in disbelief as the fox's power heals Naruto's wounds.