Don Quixote Volume 1, Chapter 30
Sancho quickly jumps in and says that was none other than Don Quijote, and explains how he tried to stop him, but he wouldn't listen. Don Quijote defends himself angrily citing the rules of knight errantry as his defense and pulls down his old helmet.
Dorotea soothes Don Quijote's ruffled feathers by assuring Don Quijote, that had the priest but known this he would never have spoken of it and the priest concurs. Don Quijote asks Dorotea for the particulars of her situation. She tells him that her father, Tinacrio the Wise, had much knowledge of magic and was able to see into the future. He knew that upon her parent's death, the giant -- Cross-eyed Pandafilando, would attack the kingdom to gain control. To avoid the slaughter of the good citizens, he instructed her not to defend the country; but seek out a knight errant in Spain named Don Quijote who has a gray, hairy mole on his back (as indeed Don Quijote does!). Also, she is to marry the knight once he cuts off the giant's head and give him the kingdom and herself.
Don Quijote explains that he cannot marry her and Sancho goes berserk yelling at Don Quijote and saying Dulcinea doesn't compare to Dorotea. Don Quijote hits Sancho with his lance twice and would have killed him if not stopped and then goes on to give him a good tongue lashing. Hiding behind Dorotea's mule, Sancho still insists that he should marry Dorotea and then he can always change his mind and return to Dulcinea. He adds that they are both good lookers even though he has never seen Dulcinea. But, the inconsistency that Don Quijote notices, is that Sancho is supposed to have just delivered a letter and spoken with Dulcinea. Sancho manages to cover up his slip of the tongue -- enough to stop Don Quijote from becoming suspicious, and they make up.
Cardenio and the priest discuss Don Quijote's madness and how if you stay clear of the subject of knight errantry you would take him for a very sensible, calm intelligent man. Don Quijote asks Sancho for more details of his visit with Dulcinea and Sancho admits leaving the letter behind and Don Quijote admits knowing he did. Sancho tells him that, luckily, he had memorized it and was able to dictate it out to a priest.