Rachmaninoff had a little help with a fugue exam at the Moscow Conservatory in 1891:

By mistake the examinations of Rachmaninoff in both piano and fugue were scheduled for the same day and hour, so his fugue examination was transferred to the following day, when he was to be examined alone, the rest of the class taking it on the regular day.  On his way home from the piano examination he saw Arensky and Safonov in a lively discussion.  As he came up to them, he heard that they were speaking of the theme for the general examination in fugue that day.  Arensky stopped Rachmaninoff to tell him that he didn't want to come to the Conservatory next morning just to give him the theme, so he dictated the fugue problem to him right there.  Safonov had stepped aside, and began to whistle the proper fugal treatment of the theme – and Rachmaninoff never knew whether this help was unintentional or deliberate.  In any case, as Rachmaninoff later learned, none of the class had found the right answer.  Only he, with this sidewalk coaching, passed the examination with a "5".

Cited in: Bertensson, Sergei & Leyda, Jay (2001) Sergei Rachmaninoff: A Lifetime in Music.  Bloomington: Indiana University Press, pp.33-34.