Fyodor Dostoyevsky, Crime and Punishment
, Part I, Chapter III (tr. Constance Garnett):
"But why is it you do nothing now?"
"I am doing . . ." Raskolnikov began sullenly and reluctantly.
"What are you doing?"
"Work . . ."
"What sort of work?"
"I am thinking," he answered seriously after a pause.
Nastasya was overcome with a fit of laughter. She was given to laughter and when anything amused her, she laughed inaudibly, quivering and shaking all over till she felt ill.
"And have you made much money by your thinking?" she managed to articulate at last.