My silence with regard to your intentions about Tristan might easily lead to a misunderstanding, dear Master, to prevent which I am now going to explain to you briefly my personal opinion. I have had a most trying time and some really bitter moments with the Vogls. But all the same, after these last rehearsals (with orchestra)—although we shall of course need many more—I can defend the official performance of the work from a musical standpoint. I cannot see in this any profanation of it, but, on the contrary, a significant act, a proof of what goodwill and enthusiasm, goaded on by categorical orders from All-Highest quarters, can do. I could not therefore conscientiously send in my resignation on the ground you suggest—namely, that I was obliged to lay down my baton on account of the clash between a sense of duty and a sense of honour. Forgive me for opposing you. I cannot admit that my doing so implies a lack of piety towards your work.
PS. Fischer was surprisingly excellent as Kurwenal (we might give him Alberich, particularly as there is no one else anywhere). Bausewein is certainly more correct musically and less lackeyish than Zottmayr.
Source: Letters of Hans von Bülow to Richard Wagner, Cosima Wagner, His Daughter Daniela, Luise von Bülow, Karl Klindworth, Carl Bechstein, ed. Richard Count Du Moulin Eckart, trans. Hannah Waller, ed. Scott Goddard (Alfred A. Knopf, 1931), No. 295