From the chapter "Seventh Week: Mindfulness in Thinking" of Andrew Weiss's Beginning Mindfulness:

There is a story about a Zen student who kept pestering his teacher to tell him the secret of awakening. After being asked so many times, the teacher finally got annoyed. He said to his student, "You know the space between your thoughts?" The student eagerly answered, "Yes, yes!!" The teacher said, "Well, make it larger!" ...

^z - 2013-10-15