Otto Klemperer met Gustav Mahler when he had the opportunity to conduct the off-stage brass at a performance of the latter’s Second Symphony in 1905. The two became friends, and Mahler helped Klemperer become the conductor of the German opera company in Prague two years later. Klemperer, in turn, became one of the foremost interpreters and champions of Mahler’s music.
Later, Klemperer recalled an incident that occurred when Mahler was conducting in Vienna:
There were few soloists in the Phiharmonic’s concerts at this period, and only the very best got a chance to appear. Mahler engaged [Ferruccio] Busoni, for instance, to play Beethoven’s Concerto in E Flat Major. Traveling down from Berlin on the night express, Busoni reached Vienna just after 9:00 a.m. to find a message awaiting him at his hotel. It said to report to the Opera House at once, where Direktor Mahler had something important to tell him.
Without breakfasting, washing or shaving–a circumstance he found highly distasteful–he rushed to the Opera House. Mahler kept him waiting for an hour, then burst from his office and extended his hand. “Not to fast in the last movement, Herr Busoni–all right?” he said, and whistled the main theme. Then with an “Auf Widersehen! he vanished again.