"Special Training!!" (特別な修業!!, Tokubetsuna Shugyō!!) is chapter 315 of the original Naruto manga.
Kakashi explains that, although combining shape transformation and nature transformation usually takes years, Naruto will be able to do so in a fraction of the time by training with shadow clones. Kakashi then demonstrates how shadow clones transfer what they learn during their existence back to the originator when they disperse. Having never noticed this before, Naruto asks if training with hundreds of clones to learn things a hundred times faster is how Kakashi became so strong. Kakashi replies that only Naruto can do this sort of training because he has access to the Nine-Tailed Demon Fox's chakra. Yamato joins them to help Naruto keep the fox in control. Before Naruto can start on his new technique, they must first determine his nature affinity; it is wind release.