The Muse is beginning to visit me. [...] The first thing that came to me was a melody, which at first I didn't in the least know how to place, until all at once the words for it came to me from the last scene of Siegfried. A good omen! Yesterday, too, the opening of the second act dawned upon me—as "Fafner's Rest," which gave me a humorously cosy motif. [...]
Source: Letters of Richard Wagner, Vol. 1, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 336