The Zen warnings come at the close of the Gateless Gate, a collection of 48 Chan (Zen) koans compiled in the early 13th century by the Chinese Zen master Wumen Huikai (無門慧開; Japanese: Mumon Ekai; 1183–1260). Wumen’s preface indicates that the volume was published in 1228.
To obey the rules and regulations is to tie yourself without a rope.
To act freely and without restraint is heresy and deviltry.
To be aware of the mind, making it pure and quiet, is the false Zen of silent contemplation.
To arbitrarily ignore causal relations is to fall into a deep pitfall.
To abide in absolute awakening with no darkening is to wear chains with a yoke.
Thinking of good and evil is being in heaven and hell.
To have views about the Buddha and the Dharma is to be imprisoned inside two iron mountains.
Becoming aware of consciousness at the instant it arises is toying with the soul.
Practicing concentration in quiet sitting is an action of devils.
If you go forward, you will go astray from the essence.
If you go back, you oppose the principle.
If you neither go forward nor back, you are a dead man breathing.
Tell me now, what will you do?
Make the utmost effort to attain full realization in this life! Do not abide in misery forever.