The Once and Future King Book 1, Chapter 9
When Arthur wakes up in his own bed the next morning, Kay is angry because he knows Arthur went out without him. They fight, but then Arthur asks Merlyn to include Kay in later adventures. Merlyn says he cannot do this, because he was only sent to educate Arthur, even though that might not seem fair. Arthur protests, and Merlyn tells him a story about a kind man who has bad luck and a cruel man with good luck. In the story, it turns out that what happens to each man is actually part of God's greater plan. In the story, a rabbi says, "Say not therefore to the Lord: What doest thou? But say in thy heart: Must not the Lord of all the earth do right?" Book 1, Chapter 9, pg. 85 Arthur does not understand this, and Merlyn gets angry, but agrees that he can do some small magic for Kay. He tells the boys to follow a path near the castle after breakfast.