[...] The third act [of Tristan] is begun. It has become clear to me that I shall never again invent anything new. This springtime of my powers has brought me such a wealth of buds that for the future I need only turn back to my store and, with a little care, coax them into bloom. Also I feel that this apparently most painful act will not exhaust me so terribly as might have been supposed. The second act prostrated me. In it the towering fires of life burned in me with such unutterable heat and brilliance that they almost scorched and consumed me. Towards the close of the act, as they sank and died and the soft radiance of transfiguring death glowed from the embers, I grew calmer. I will play you this part if you come.—I have good hopes of the end now! [...]
Source: Letters of Richard Wagner, Vol. 2, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 404