Heze Shenhui was the first to emphasise "awareness/knowing" in Chan and connected it with the practice of no-thought. This was later followed by practically every later Chan teacher but mostly by Guifeng Zongmi, Yongming Yanshou and Pojo Jinul. This teaching on awareness is easily misconstrued as an atman similar to Sankhya and other essentialist views. What shows that awareness is not an ultimate soul is the practice (see: Essential Zen Practice) where it is not that one finds something eternal but does not abide in anything. Thus it is in harmony with the fundamental teachings of the Buddha on emptiness. Zen is a very practical path, therefore when one wants to compare it to non-Buddhist philosophies it is understandable that those ignorant of the doctrinal teachings confuse it with wrong views.
"The term “Owner” is used here to mean the non-birth-and-death essence within this body composed of the five aggregates. This essence will fully manifest itself when one’s feelings, conceptions, mental formations, and consciousness calm down. It is never apart with these aggregates, but when they are operating, we rarely realize this essence. The Owner is the tranquil, aware essence that has never been agitated, changed, or eradicated. To experience it, try this contemplation: When meditating or sitting alone at a quiet place, note how your feelings, conceptions, mental formations, and consciousness calm down, yet your eyes, your ears, etc., are full of awareness. Then, ask yourself, “Who is it that is seeing, hearing, etc.? Is it the permanent, tranquil, aware nature inside?” Therefore, the theory of “the Owner” mentioned here does not contradict the Buddha’s teaching about no self. When we have real experiences, we know it. It is useless to hang on to or argue over theories."
(Thich Thanh Tu: Keys to Buddhism, p 57-58)
"Foreign dust illustrates false thinking, and voidness illustrates self-nature, that is the permanent host who does not follow the guest in the latter's coming and going. This serves to illustrate the eternal (unmoving) self-nature which does not follow false thinking in its sudden rise and fall. Therefore, it is said: 'if one is unmindful of all things, one will meet with no inconvenience when surrounded by all things.' By dust which moves of itself and does not inconvenience voidness which is cleafly still, one means that false thinking rises and falls by itself and does not hinder the self-nature which is immutable in its Bhutatathata (suchness, thatness) condition. This is the meaning of the saying: 'If the mind does not arise, all things are blameless.'
If there is singleness of thought abiding in that 'which is not born and does not die', without pursuing sound and form, this is 'going against the stream'; this is called 'looking into the hua t'ou' or 'turning inwards the hearing to hear the self-nature'."
(Hsu Yun: The Ch'an Training)
"The bodhi mind is replete within us. If we look for it elsewhere, we will not find it. Just as a Chan patriarch said, “To move the mind is to err, to raise a thought is to stray.” As soon as we look for it we lose it; it is like looking for an ox while riding an ox; we are already sitting on its back, but we do not know it. It is also like looking for a shadow at midday. At this moment, when you are listening to this teaching, the mind that does not raise a single thought is the profound and clear bodhi mind. A mind with no-thought is the mind of total clarity, knowing, and awareness, without a single bit of delusion, drowsiness, or scattered thoughts. When we realize this mind that is unborn and undying, we attain enlightenment."
(Wei Chueh: From Bodhi Mind to Ultimate Enlightenment)
"Since all dharmas are like dreams or phantoms, deluded thoughts are originally calm and the sense-spheres are originally void. At the point where all dharmas are void, the numinous awareness is not obscured. That is to say, this mind of void and calm, numinous awareness is your original face. It is also the dharma-seal transmitted without a break by all the Buddhas of the three time periods, the successive generations of patriarchs, and the wise advisors of this world. If you awaken to this mind, then this is truly what is called not following the rungs of a ladder: you climb straight to the stage of Buddhahood, and each step transcends the triple world."
(Pojo Jinul: Secrets on Cultivating the Mind in "Collected Works of Chinul", p 145)