From Autobiography of Mark Twain: The Complete and Authoritative Edition, Volume 3, edited by Benjamin Griffin, et al.
"I reserved the privilege of reading and talking gratis, for charities, when I should wish to do it, but I was resolved never to talk for pay again. I have read and talked many times since, in these eleven years, but never for pay. It is a delight to read and talk when one is not charging anything for it, for that condition sets you free from all sense of responsibility, and you are quite sure to have a good time."
From Dictated October 11, 1907