I cannot understand in what manner I have caused YOU grief, but I feel the painful rebound of your wounded heart. My admonition to T. proceeded from a pure cause. X. himself knew nothing of it, and T. would have done well if he had kept silence towards you. "Insinuations" and "diplomacy" are surely out of the question. I greatly dislike mixing myself up with other people's affairs, and if I have done so this time, it was certainly not because I was led to it by others (I give you my word, that not a word has been said or written about the whole matter), but merely because it had been imposed upon me as a kind of duty to act as guardian to T., and it appeared only too probable that his conduct had not been very correct. The young Titan sometimes gives way to an absence of mind and a state of overexcitement, against which those who wish him well should warn him. His exceptional talent and his genial and prepossessing manner generally incline me towards being overindulgent with him, and I do not deny my genuine love and partiality for this remarkable specimen of a "Liszt of the future," as T. has been called at Vienna. But for that very reason I expect him to be a good and steady fellow in all respects. Be thanked for the kindly friendship and care you bestow upon him. I hope he will not only profit by them, but honour them. The rare happiness of living near you, and of being distinguished by you, should form and mature him as an artist and as a man.
Franz Liszt
Source: Project Gutenberg eBook #4234, Correspondence of Wagner and Liszt — Volume 2, No. 263