I think it was one of the earlier episodes but I can't remember. Maybe it was during a character's backstory or a flashback but it was only in 1 episode.
There was an episode in FMA Brotherhood where the scene would fade to a black screen with white Japanese text appearing vertically, and then fades back to the story, and the whole process is repeated several times throughout the episode as the story progresses. I thought it was during the Ishvalan extermination episode, but Riza Hawkeye was narrating that part so I don't know what other episode it could be.