J’ai un alto merveilleux, me dit-il, un instrument admirable de Stradivarius, et je voudrais en jouer en public. Mais je n’ai pas de musique ad hoc. Voulez-vous écrire un solo d’alto? je n’ai confiance qu’en vous pour ce travail.
Composer Hector Berlioz was friends with the famous violinist Paganini. When the latter managed to get his hands on a Stradivarius viola (later called the Paganini-Mendelssohn) he wanted to play it in public, and asked his friend Berlioz to create something nice. The resulting Adagio didn’t suffice, so he rejected it, disappointed.
Years later the same Paganini visited a performance of this very piece: Harold in Italy. It touched him so much he kissed the hand of the composer after the concert, before an astounded audience. It was the piece he commissioned years before, and Paganini paid him after all.