This verse is titled “On Zen.” I found it on page 464 of James H. Austin’s 2006 book, Zen-Brain Reflections.
A reality exists, even before heaven and earth;
It has no form, much less a name.
Eyes fail to see it. No voice has it for ears to hear.
To call it ‘‘Mind’’ or ‘‘Buddha’’ violates its nature.
For then it becomes like some visionary
flower in the air.
It is not ‘‘Mind’’ nor ‘‘Buddha.’’
It is absolute quiet, yet illuminating in
a mysterious way.
It allows itself to be perceived only
by the clear-eyed.
It is Dharma, truly beyond form and sound.
It is Tao, having nothing to do with words.
Once, wishing to entice the blind,
the Buddha playfully let words escape his golden
mouth. Ever since, heaven and earth have become full
of entangling briars. Oh my good worthy friends
gathered here, if you wish to hear the thunderous
voice of the Dharma, exhaust all your words,
empty all your thoughts.
For only then may you come to realize, at last,
this one essence.
(By Daio Kokushi, 1235–1309, tr. D. T. Suzuki, in Manual of Zen Buddhism.)