"A Message from the Heart" (心の中の手紙, Kokoro no Naka no Tegami) is episode 275 of the Naruto: Shippūden anime.
As Naruto voices his concern that he has been sensing the Nine-Tails' chakra outside for a while now, B tries to allay his suspicions telling him that this was impossible as they were in a Chakra Isolation Chamber, while conversing with the Eight-Tails about the Gold and Silver Brothers who had seemingly been reincarnated. Making an excuse that he needed to use the bathroom, Naruto leaves the chamber before B could realise what he was up to and stop him. He is however noticed by two guards who alert headquarters. Upon hearing the news, HQ tells them to deploy the guard detail and Naruto is confronted by Shibi Aburame who tells him he cannot allow him to go any further. Out of the group, Iruka emerges shocking Naruto and tells Shibi that he would speak to the young man. Not believing their story, Naruto — who enters Sage Mode — demands to be let outside and when confronted by the two Akimichi guards, breaks through their defence and reaches outside. He is however halted by the Nara's Shadow Imitation Technique but not before his sensory skills in Sage Mode activates giving him a full perception of what was happening on the battlefield. Shocked at what was happening, Iruka tells Naruto the truth but at the same time, erects a barrier to stop Naruto from leaving. The young man however enters the Nine-Tails Chakra Mode and easily breaks the barrier, the link to the shadow and Shibi's kikaichū and heads for the battlefield while fixing his forehead protector and finding the note Iruka had left him. After B and Iruka bump fist and have a brief conversation, B sets out after Naruto. With the Kumo Barrier Team alerted and the Self-Repairing Barrier prepared, the two jinchūriki using the Tailed Beast Ball are able to break through the barrier despite the team's best efforts.