" An exquisite morning, my dear child ! Three days I had been at the passage, " Whom you embraced, whom you have smiled upon," etc. There was a long check to my inspiration, and, in trying to compose the passage, I could not recall just how I had planned it. I was upset; I could not con- tinue. A little goblin knocked at my door and appeared to me disguised as the lovely Muse. In a moment the problem was solved. I went to the piano and wrote out the passage as rapidly as if I had it by heart. Whoever listens to it critically will discover something familiar in it. " Dreams " haunts it. But you will forgive that, dearest! No, do not repent having loved me ! It is heavenly !"
The abridged letters between Wagner and Mathilde Wesendonck, translated by Gustav Kobbe. If you have never read these fascinating letters this might be a good place to start.