Gutei’s Finger
Whatever he was asked (concerning Zen) Gutei simply stuck up one finger. At one time he had an acolyte, whom a visitor asked, “What is the essential point of your master’s teaching?” The boy just stuck up one finger. Hearing of this, Gutei cut off his finger with a knife. As the boy ran out of the room screaming in pain, Gutei called to him. When he turned round his head, Gutei stuck up one finger. The boy suddenly became enlightened.

When Gutei was about to die, he said to the assembled monks, “I received this one-finger-Zen from Tenryu. I used it all my life, but did not exhaust it.” When he finished saying this, he entered into his eternal rest.

The Commentary
The origin of the enlightenment of Gutei and the boy is not in the finger itself. If you understand this, Tenryu Gutei, the boy, and you yourself are all run through with one skewer.

The Verse
Gutei made a fool of old Tenryu (or, Gutei and Tenryu made a fool of everybody).
The sharp blade has damaged the boy.
The Mountain-Spirit raised his hand and lo, without effort,
The thousand, myriad-piled mountain are split into two, Kasan (and Shuyo).

As translated by R.H. Blyth