[...] It is not possible for me to take leave of you to-day after this third and, provisionally, last performance of Tristan, without once again expressing my gratitude. No artist, indeed, can ever have been animated by more inspiring emotions than have been mine in the course of my association with you. Not even the mother rejoicing over the child whom she has with pain brought into the world, can feel such rapturous gratification as was mine to the full when your exquisite performance gave to my ears the warm living tones of the score that had for so long lain dumb before me! An attempt on my part to praise your most significant, your incomparable achievement, would merely be an intrusion upon your own glorious consciousness of the same. [...] While I breathe, it will be one of the dearest concerns of my heart to prove my love for you and how filled I am with gratitude to you! [...]
Source: Letters of Richard Wagner, Vol. 2, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 607