“There are nowadays professors of philosophy, but not philosophers.”

Source: Zen and the Art of Motorcycle Maintenance (1974), Ch. 29
Context: The Professor of Philosophy has made a mistake. He's wasted his disciplinary authority on an innocent student while Phædrus, the guilty one, the hostile one, is still at large. And getting larger and larger. Since he has asked no questions there is now no way to cut him down. And now that he sees how the questions will be answered he's certainly not about to ask them.
The innocent student stares down at the table, face red, hands shrouding his eyes. His shame becomes Phædrus' anger. In all his classes he never once talked to a student like that. So that's how they teach classics at the University of Chicago. Phædrus knows the Professor of Philosophy now. But the Professor of Philosophy doesn't know Phædrus.

Drawn and Quartered (1983)

Source: Zen and the Art of Motorcycle Maintenance (1974), Ch. 29
Context: The Professor of Philosophy has made a mistake. He's wasted his disciplinary authority on an innocent student while Phædrus, the guilty one, the hostile one, is still at large. And getting larger and larger. Since he has asked no questions there is now no way to cut him down. And now that he sees how the questions will be answered he's certainly not about to ask them.
The innocent student stares down at the table, face red, hands shrouding his eyes. His shame becomes Phædrus' anger. In all his classes he never once talked to a student like that. So that's how they teach classics at the University of Chicago. Phædrus knows the Professor of Philosophy now. But the Professor of Philosophy doesn't know Phædrus.

On My Philosopy (1941)
Context: My path was not the normal one of professors of philosophy. I did not intend to become a doctor of philosophy by studying philosophy (I am in fact a doctor of medicine) nor did I by any means, intend originally to qualify for a professorship by a dissertation on philosophy. To decide to become a philosopher seemed as foolish to me as to decide to become a poet. Since my schooldays, however, I was guided by philosophical questions. Philosophy seemed to me the supreme, even the sole, concern of man. Yet a certain awe kept me from making it my profession.

E. Payne, trans. (1974) Vol. 1, p. 347
Parerga and Paralipomena (1851), Aphorisms on the Wisdom of Life

Variant: To make light of philosophy is to be a true philosopher.
Source: Pensées

The Righteous Mind (2012)

“Selected Aphorisms from the Athenaeum (1798)”, Dialogue on Poetry and Literary Aphorisms, Ernst Behler and Roman Struc, trans. (Pennsylvania University Press:1968) #96
Athenäum (1798 - 1800)

Theaetetus, 155d
Plato, Theaetetus