Ludwig Van Beethoven, John Trie (2017). “Ludwig Van Beethoven for Classical Guitar - Tablature: Arranged for Guitar by John Trie”, p.36, BoD - Books on Demand
Attributed to Ludwig van Beethoven by Bettina von Arnim in a letter to Goethe (May 28, 1810), as quoted in Bettina von Arnim "Goethe's Correspondence with a Child", 1835.
Ludwig van Beethoven, Friedrich Kerst, Henry Edward Krehbiel (1964). “Beethoven, the Man and the Artist, as Revealed in His Own Words”, p.13, Courier Corporation