What is Legendary Sannin?
The name given to the genin cell of Sarutobi Hiruzen, consiting of Jiraiya, Orochimaru and Tsunade. During the Second Great Shinobi War, they battled Salamander Hanzou, the leader of Hidden Rain to a standstill. Hanzou was so impressed with their abilities to survive the battle, he spared their lives on the condition they accept the title of "Sannin of Konoha". Over time, their skills grew even further and they gained a wide reputation as Konoha's Legendary Three.
The three of you are strong. Even within this strife, you survived.
I, Hanzou... hereby honour you as the "Sannin of Konoha."
The Three Legendary Ninbja
Legendary Sannin:; The three ninja, Jiraiya, Tsnuade, and Orochimaru, who faced off against Hanzo of the Salamander when they were Chuunin.
They fought so well he wrote "The Legend of the Sannin"