Insert a superscript at the end of your music example title and supply a corresponding footnote. The footnote gives publication information about the score you used for your example.
The note for the above example is:
5. Johann Sebastian Bach, Bach-Gesellschaft Ausgabe, vol. 15, Drei Toccaten für Orgel, ed. Wilhelm Rush (Leipzig: Breitkopf und Härtel, 1867): 258.