The Red and the Black, Volume 1, Chapter 26, “The World, Or What the Rich Lack.”
After several months of application kept up at every moment, Julien still had the air of a thinker. His way of moving his eyes and opening his lips did not reveal an implicit faith ready to believe everything and uphold everything, even by martyrdom. It was with anger that Julien saw himself surpassed in this respect by the most boorish peasants. They had good reasons for not having the air of thinkers.
Or in the French (corrected, with thanks to Sasha Volokh):
Après plusieurs mois d’application de tous les instants, Julien avait encore l’air de penser. Sa façon de remuer les yeux et de porter la bouche n’annonçait pas la foi implicite et prête à tout croire et à tout soutenir, même par le martyre. C’était avec colère que Julien se voyait primé dans ce genre par les paysans les plus grossiers. Il y avait de bonnes raisons pour qu’ils n’eussent pas l’air penseur.
I feel strangely compelled to add the following confession. I just finished re-reading The Charterhouse of Parma. I have always supposed, following everyone else so far as I can tell, that it is a greater work than The Red and the Black. But it has been a very long time since I read Charterhouse. And, I’m slightly embarrassed to say, I find upon re-reading that I much prefer The Red and the Black. Fabrizio seems so much less interesting than Julien, and fond as I am of Clelia, I am much, much more fond of Mathilde and Madame de Renal. (I have, since I was young, been in love with Mathilde de la Mole, and always will be.)