Transcript:
Schroeder sits at the piano playing complex notes.
Charlie Brown approaches and says to Patty,"See? Isn't it amazing?" She asks, "What's he playing? Bach?"
They sit across from Schroeder. Charlie Brown says,"Oh, no, this is one of his own compositions..."
He concludes,"'Rhapsody on a theme by Schroeder'!"
Original comic:
I couldn't find anything. Tried asking an llm and the best it could say was probably something by Liszt or Rachmaninoff. It did offer to draw the comic and the sheet music side by side, which produced this unintentionally funny hallucination: