"French Music: From the Death of Berlioz to the Death of Fauré". Book by Martin Cooper (p. 136), 1951; later quoted in "Debussy and Wagner", book by Robin Holloway (p. 207), 1979.
Claude Debussy's statement of 1910, as quoted in "Debussy on Music" edited and translated by Francoise Lesure and Richard Langham Smith (p. 243), 1977.