A Conversation with the Fourth!! (四代目との会話!!, Yondaime to no Kaiwa!!) is chapter 440 of the Naruto manga.
Naruto picks up on the Fourth Hokage's claim that he is his son. Naruto is overjoyed and follows his father to a part of his subconscious where the Nine-Tails is not threatening to kill them both. The Fourth explains that he had designed Naruto's seal to produce an imprint of him if ever the seal was about to break. Naruto asks why the Fourth would seal the Nine-Tails within his own son. The Fourth responds that he trusted only his son to master the Nine-Tails in order to defeat the masked man responsible for its attack on Konoha sixteen years earlier. They discuss Pain's ideas about peace and the Fourth suggests that he is a product of the war-torn era he grew up in, something the masked man is likely taking advantage of. The Fourth encourages Naruto to find his own solutions about peace and Pain. After restoring the seal, he disappears.