"[The Quartet] was rehearsed frequently under Beethoven's own eyes: I said Beethoven's eyes intentionally, for the unhappt man was so deaf that he could no longer hear the heavenly sound of his compositions. And yet rehearsing in his presence was not east. With close attention his eyes followed the bows and therefore he was able to judge the smallest fluctuations in tempo or rhythm and correct them immediately. At the close of the last movement of this quartet there occurred a meno vivace, which seemed to me to weaken the general effect. At the rehearsal, therefor, I advised that the original tempo be maintained, which was done, to the betterment of the effect.
Beethoven, crouched in a corner, heard nothing, but watched with strained attention. After the last stroke of the bows he said, laconically, 'Let it remain so,' went to the desks and crossed out the meno vivace in the four parts."
- a Hungarian violinist, recounting a rehearsal of the Op. 127 quartet with Beethoven present.
Quote from Performing the Beethoven Quartets in Their First Century by Robert Winter, an essay in The Beethoven Quartet Companion (1994), p. 40