[...] It has certainly not escaped my notice that Mme. Schefsky is not an entirely "finished product," but, after all, I am obliged to trust that nearly all my singers will allow me to instruct them in a great many matters of which they previously knew nothing. The basis of everything is the most painstaking accuracy, particularly in rhythm. I demand (from Tannhäuser onwards) that my singers shall put "recitative" entirely out of their minds and learn to sing my notes in strict time down to the most minute fraction of their melodic value as the only means of arriving at an understanding of the way I intend they should be sung. Well, you know all about that. [...]
Source: Letters of Richard Wagner, Vol. 2, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 689