Shoyoroku - Case 72: Chuyu's "Monkey"

Kyozan [1] asked Chuyu,
  "What does buddha-nature mean?"
Chuyu said,
  "I will explain it for you by allegory. Suppose there is a room with six
   windows. Inside there is a monkey. Outside, someone shouts, 'Monkey!
   monkey!' It immediately responds. If someone calls, 'Monkey!' through any
   of the windows, it responds just the same. It is just like that."
Kyozan said,
  "How about when the monkey is asleep?"
Chuyu descended from his Zen seat, grasped Kyozan and said,
  "O monkey, monkey, there you are!"

[1]: At this time Kyozan was about 13 years old.