Tsunade's Warning: Ninja No More!

is episode 98 of the original Naruto anime.

Summary
Konohamaru is visibly saddened by the fact that his grandfather's things were being removed from the Hokage's office because of the new Fifth Hokage. As Konohamaru rushes up the stairs of the Academy to stop them, he accidentally runs head-first into Tsunade's bust.

Later, Tsunade goes to the hospital, to heal Sasuke Uchiha, Rock Lee and Kakashi Hatake. She heals both Sasuke and Kakashi then proceeds to examine Lee. With regret, she tells Lee that he will have to end his career as a shinobi as some of the injuries were far too grave and the chances of him surviving the operation were slim. Upon hearing the news, Lee walks out of the room contemplating what Tsunade just told him.

Trivia

 * The segment in which Konohamaru runs into Tsunade's bust is removed in the English dub.