Inheritance! The Necklace of Death!

is episode 91 of the original Naruto anime.

Synopsis
Naruto tries to hit Tsunade with his not yet perfected Rasengan. As expected, Tsunade dodged it easily, then berate Jiraiya for trying to teach Naruto a technique that he couldn't possibly master. Naruto insisted that he could, and bet that he could learn it in three days. Naruto's personality reminded Tsunade of her deceased loved ones, so she accepted the bet, giving Naruto a week. If Naruto won, she would accept that he could become Hokage, and would give him her incredibly valuable necklace that had originally belonged to the First Hokage. Naruto accepted.

Later, Shizune talked to Naruto about Tsunade's past and about the history of the necklace. Shizune said that the necklace wasn't an ordinary necklace. If anyone except Tsunade wore it, the person would die. While Shizune was talking to Naruto, Tsunade was sitting on top of the gate of Tanzakugai, thinking of her past.