The following passage from chapter XVI of Book I of the novel Le rouge et le noir (The Red and the Black) by Stendhal refers to "un dicton de province", that is, at some kind of saying or proverb (emphasis mine):
Elle quitta le jardin de bonne heure, et alla s'établir dans sa chambre. Mais ne tenant pas à son impatience, elle vint coller son oreille contre la porte de Julien. Malgré l'incertitude et la passion qui la dévoraient, elle n'osa point entrer. Cette action lui semblait la dernière des bassesses, car elle sert de texte à un dicton de province.
This is rendered this way in the translation by Robert M. Adams:
She left the garden early, and retired to her bedchamber. But, unable to control her impatience, she came and pressed her ear against Julien's door. In spite of the uncertainty and violent passions that were devouring her, she dared not enter. Such an action seemed to her the last word in crude behavior, simply because it provides the text of a provincial proverb.
My question is: which saying or proverb is Stendhal referring to in this passage? I believe it's important to fully understand the meaning of the last sentence.