Pretty sure it's a decently famous song. It's been stuck in my head and this is the only part I know, and I really want to find it online but I have absolutely no idea what it's called. I'm probably playing it wrong so hopefully it's recognizable. Song (hopefully that link works)
(pssst I'm posting this on more than one forum because I don't imagine many people can name classical music)
Edit: Someone was able to find the song I was thinking of! It's Bach's Prelude.