[...] I am very touched that you set so high a value on a first performance of Tristan. But listen, my friend, how matters stand. I cannot let this most intimate work be performed at all, unless it can first be done in my personal presence and under my direction. That is absolute. Well, the Grand Duke of Baden, whose amiable young wife has taken a special interest in me, has succeeded, after repeated efforts, in gaining me the prospect (through Dresden) of being allowed to visit a stated place in Germany for a stated period for the one and only purpose of producing a new work for the first time. You will understand no doubt that this place must now be Karlsruhe. The only thing I can do towards fulfilling your friendly wish is to put the opera in your hands so that you can give it immediately afterwards. Perhaps I may come myself to you a week after the Karlsruhe performance and hear yours.
[...] For the rest I can only wish that you will be pleased with the opera and find it suitable to your purpose. The libretto will soon be published and many people will probably rub their eyes over it, and in particular wonder how I am composing this or that—I have been disgracefully interrupted in my work. I am only just resuming it, and there is no question of its being finished before the end of winter. [...]
Source: Letters of Richard Wagner, Vol. 2, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 371