What did Tokusan see when Ryūtan blew out the candle? To answer this, we have to first consider who Tokusan had been before meeting with his teacher.
Previous to his encounter with Ryūtan, Tokusan Senkan boasted that he had mastered the meaning of the Diamond Prajñā Sutra. He sometimes called himself “Shū, King of the Diamond Sutra.” He was reputed to be especially well versed in the myriad commentaries on the sutra, of which he himself had produced over 1,5000 pounds. It appears that there was no other lecturer to match him.
One day, he hears that there is a teaching in the South being passed from successor to successor that points directly at the mind and does not rely on the scriptures. Angered beyond endurance at this, he crosses mountains and rivers, carrying his sutras and commentaries with him, intending to set the record straight with those upstarts once and for all. On the way, he stops for a rest by the side of the road and soon an old woman comes along and also stops for a rest beside him.
Tokusan asks, “What kind of person are you?”
The old woman says, “I am an old woman who sells dumplings.”
Tokusan says, “Will you sell some dumplings to me?”
The old woman says, “Why does the master wish to buy dumplings?”
Tokusan says, “I would like to buy dumplings to refresh my mind.” (This apparently is something of a pun, as the Chinese words for generic dumplings - dim sum - also mean "refresh mind.")
The old woman says, “What is that great load the master is carrying?”
Tokusan says, “Have you not heard? I am Shū, King of the Diamond Sutra. I have mastered the Diamond Sutra. There is no part of it that I do not understand. This load I am now carrying is commentaries on the Diamond Sutra.”
Hearing his insistence, the old woman says, “This old woman has a question. Will the master permit me to ask it?”
Tokusan says, “I give you permission at once. You may ask whatever you like.”
The old woman says, “I have heard it said in the Diamond Sutra that past mind cannot be grasped, present mind cannot be grasped, and future mind cannot be grasped. Which mind do you now intend somehow to refresh with dumplings? If the master is able to say something, I will donate a dumpling. If the master is unable to say anything, I will not to much as even sell him a dumpling.”
Tokusan is dumbfounded at this: he does not know how he might politely reply. The old woman just swings her sleeves contemptuously at him and gets up to leave. Tokusan, realizing that he must be in the vicinity of a great dharma teacher, asks her for directions and is pointed toward the temple of Zen Master Shin of Ryūtan.
After the candle was blown out, Tokusan praised his teacher and then set fire to his voluminous commentaries on the Diamond Sutra.