Once you have settled your posture and regulated your breathing, you should relax your abdomen.
Do not think of any good or evil whatsoever.
Whenever a thought occurs, be aware of it – as soon as you are aware of it, it will vanish. If you remain for a long period, forgetful of objects, you will naturally become unified.
This is the essential art of tso-ch’an (Zazen).
Honestly speaking, tso-ch’an is the dharma gate of ease and joy. If there are many people who become ill [from its practice], it is because they do not take proper care.
– Dogen’s Manuals of Zen Meditation, Carl Bielefeldt, p181