Final answer:
The painting rejected by the Salon in 1863 was Édouard Manet's The Luncheon on the Grass, which was later displayed at the Salon des Refusés.
Step-by-step explanation:
The painting that was rejected by the Salon in 1863 was Édouard Manet's The Luncheon on the Grass (Le déjeuner sur l'herbe). The controversial canvas depicted a nu-de female alongside clothed males in a picnic setting, a juxtaposition that scandalized the Parisian public.
Due to the rejection, Manet exhibited the piece at the Salon des Refusés, which was established for artworks not accepted by the official Salon. After the uproar caused by The Luncheon on the Grass, the Salon jury somewhat reluctantly accepted Manet's subsequent painting, Olympia, in 1865, despite their disapproval of the subject matter, in an effort to avoid the perception of a personal attack on the artist.