The Anbu Gives Up? Naruto's Recollection (暗部もお手上げ ナルトの記憶, Anbu Mō Teage, Naruto no Kioku) is episode 198 of the original Naruto anime.
The ANBU agents use reverse hypnosis on Naruto, but realize that he remembers nothing of importance. Some of the group researches Gennō, but finds little except for him being a mediocre carpenter who did little out of the ordinary. However, it is revealed that his letter of introduction was forged, and investigation of the scene of his suicide bombing and the corpse in the hospital suggests that Gennō staged his death.