Original Mind

One who practices Zen must put a stop to all kinds of conditions and eliminate all sorts of things -- good and evil, right and wrong, self and others, mundane and supramundane. He must abandon both the body and the mind, thinking of nothing whatsoever, letting his mind go free. If one is not bound by seeing, hearing, feeling and knowing and if one is not deluded by circumstances, then, and only then, can he truly practice Zen. 

 

The Zen practitioner should understand that :

• Past things are already past. If you do not think about it, then any thought of the past vanishes; thus, there are neither any past things nor any past mind. 
• Furthermore, future things have not yet arrived; so if you do not wish for or seek anything, then any thought of the future vanishes; thus, there are neither any future things nor any future mind. 
• Finally, present things are already present, so if you are just aware without grasping at or dwelling on anything and never let a thought of love or hate arise, then the thought of the present vanishes; thus, there are neither any present things nor any present mind. 

If you can understand the mind without being fixed anywhere or on anything, just generate pure thought, neither grasping at anything nor dwelling anywhere - that is seeing one's own Original Mind; that is seeing one's own Original Nature. 

Dazhu Huihai - 8th century AD

When you practice Zen, sit in the lotus position, close your eyes, keep your body erect and allow your mind to become clear and still. Abandon any thoughts of good or evil. When thoughts do arise, just observe each thought carefully and become aware whence it arises. Then you can become aware of false thought as it suddenly arises and suddenly dies away, as it comes and goes, never stopping for one instant. 

You should have ni impulse to follow false thoughts anywhere nor  hold any idea about getting rid of it...

... In time, as the observer becomes very skilful, false thought gradually falls away until, without a single thought arising, there remains only still, clear voidness. While walking, standing, sitting and lying down, always practice in this manner...

From the Introduction to the 

Treatise on Entering The Tao of Sudden Enlightenment, 

Translated by Dharma Master Lok To