In 1853, Brahms went on a tour of German cities with the Hungarian violinist Eduard Reményi. In the town of Celle, they were scheduled to play Beethoven’s Sonata in c minor (op. 30, no. 2):
but it was found that the piano in the hall was tuned a half tone too low. Reményi refused to tune his violin down, so, rather than to disappoint the audience, Brahms obliged by transposing his part up a half tone. He played the entire sonata from memory in the key of C sharp minor.
Leonard, Richard (1961) The Stream of Music. London: Hutchinson, p. 256.