The Secret of the Mangekyō…!! (万華鏡の秘密…!!, Mangekyō no Himitsu…!!) is chapter 385 of the Naruto manga.
Knowing that not even Itachi could kill the entire Uchiha clan by himself, Sasuke asks who helped him kill their family, planning to kill them too after he is done with Itachi. Itachi doubts that he could do this, but he gives Sasuke the name of Madara Uchiha. A founder of Konoha, Sasuke asks how Madara could still be alive after so many decades. Itachi reminds him not to be deceived by such facts, having once believed Itachi to be a loving older brother. Angered that he is being patronized with genjutsu, Sasuke demands that the real Itachi face him. Itachi responds that, since Sasuke doesn't have a Mangekyō Sharingan, there is no reason why he should do so, but agrees to tell him about Madara anyway.