Source, in full
Whilst rehearsing the Alpine Symphony, referring to the theme in which he quotes and extends the theme from the slow movement of the violin concerto by Max Bruch. The quote is reported in Kurt Wilhelm, Richard Strauss - an intimate portrait. Thames and Hudson, London, 1989, page 40. The theme's major appearence is in C major just after rehearsal mark 80 ("At the summit"), played by horns in unison
Notes from Wikiquote
\clef bass \time 2/2 \key c \major \tempo "Allegro Maestoso." \partial 4 | g' -\( e2.) g4(d2.) g4(c,2 g4 f8. g16 e4 g e' d8. c16 g'4) | } .