The Fifth Gate: A Splendid Ninja is Born

is episode 50 of the original Naruto anime.

Synopsis
Lee's speed proved too much for Gaara, and his sand was no longer able to form a shield fast enough to be of use. Lee opened the Fifth Gate, and used his most powerful attack, Reverse Lotus. Unfortunately for Lee, Gaara survived this final blow by softening his fall with sand, and used the sand to crush Lee's left arm and leg. Gaara moved his sand to finish Lee, but Guy jumped in to protect his student. Lee, although unconscious due to the pain, rose to continue the battle, his desire to win fueling his broken body. Guy wept at Lee's dedication, and Lee was taken away to recover. The medical ninja announced that Lee's injuries were too severe to be completely healed, and that he would never be able to fight as a ninja again. Guy regretted teaching Lee such dangerous techniques, and vacated the ring for the final match between Chōji Akimichi and Dosu Kinuta.