From Jean Cocteau’s Opium: Diary of His Cure (Opium, journal d’une désintoxication – though I only have the translation). I’ve lost my page citation but I think it was towards the middle of the book – along with a few other notes on Proust.
I have recounted elsewhere the anecdote about the tip to the concierge at the Ritz Hotel. “Can you lend me fifty francs?” “Here you are, Monsieur Proust.” “Keep it, it’s for you.”
Needless to say, the concierge was to receive three times the amount next morning.