Participating in zen is zazen. Zazen is good being done in a quiet room. Zaniku (zabuton) should be placed. Wind and smoke should not be let in, rain and dew drops should be kept out. A place in which body and mind stays should be well maintained. Those ancestors who sat on a hard rock or on a large flat stone put lots of grass on them. A sitting place should be comfortable in the dim light, should be warm in winter and cool in summer.
Throw any conditions and stop all activities. Zazen is not regarded as goodness nor evil, not mind or consciousness nor ideas or thoughts or views. Try not even to become a buddha. Drop off either sitting or lying. Control drinking and eating. Protect and respect fast passing time. Devote to zazen as if your hair is on fire. The fifth patriarch at Mt. Ohbai did nothing but the same thing, just zazen.
During zazen wear Kesa, put zafu (cushion) on zabuton. Zafu is not placed under whole feet and waist but under half the latter part of the waist and feet. So knees touch zaniku (zabuton.) and the spine lies on zafu. This is the way Buddhas and patriarchs do zazen.
Take half cross-legged position or full cross-legged position. Full cross-legged position is to put right foot on left thigh and left foot on right thigh. The edges of the feet should be equally positioned on the thighs. For half cross-legged position just put left foot on right thigh.
Robes and clothing should be loose and neat. Put right hand on the left foot and left hand on the right palm. The tips of both thumbs are lightly touching, aligned with the navel. Hands stay close to the body.
Sit upright. Do not lean toward left or right. Do not lean forward or backward. Align ears with shoulders and nose with navel. Put tongue to the ceiling of the mouth. Breathe through nose. Lips and teeth should be closed. Open eyes not too wide nor too narrow. Exhale deeply when you start sitting.
Continue sitting with considerations on what is not thought (zazen.) How could what is not thought be considered? Non-thinking. This is the art of zazen.
Zazen is not learning zen, but the dharma gate of the great comfort, the untainted practice and enlightenment.
Written by Eihei Kigen Dogen in 1243
Translated by Eishin Ikeda, Peter Columbus, June 20, 2016