Don Quixote Volume 1, Chapter 48
The two priests discuss their views on the plays currently being staged in Spain. They all stop to eat and rest. Sancho spies an opportunity to talk to his master and try to convince him that he is being tricked, not enchanted. Don Quijote remains stubborn and insists that only supernatural powers could contain Don Quijote. Sancho, who has heard that enchanted people neither eat nor drink, plays the trump card of his argument. He asks Don Quijote if he has felt the need to urinate.
Slow on the uptake; Don Quijote finally understands what his squire is driving at and says:
"Ah, ah, now I understand you, Sancho! Oh yes, lots of times, and I feel it coming right now. Get me out of this pickle, because it's already pretty messy in here!" Volume 1, Chapter 49, pg. 333