"The Origin of Konoha" (木ノ葉のはじまり, Konoha no Hajimari) is chapter 398 of the original Naruto manga.
Sasuke doesn't want to hear Tobi's "truth" about Itachi, but Tobi insists, saying that there are too few people who know what Itachi has actually done. As this is what Itachi wanted, he attempted to kill Tobi to make sure Sasuke would never find out about the motivations that drove him to do what he did. Sasuke cannot fathom that Itachi would do anything for his benefit and passes out. When he regains consciousness, Tobi starts over. Itachi did kill the Uchiha clan, but he did so under orders from Konoha. This being only the most recent chapter in the Uchiha's history, Tobi begins by touching upon the pre-Konoha era and Madara's own relationship with the future First Hokage.