True Mind is No Mind

'Worldly wealth is subject to loss, theft, damage, decomposition, and a thousand other things. But nothing ─ not time, not natural forces, not human beings ─ can take away Dharma wealth. However, if your mind moves, the wealth is gone. Likewise, the instant your mind stops moving, you enter the door of Ch'an. And at that moment, your mind is pure; that is, there is no mind. At that moment, you instantly realize the wisdom of non-arising. Such wisdom is not subject to the cycle of birth and death.'
(The Sword of Wisdom by Sheng-yen, online p 152)

'What is called no-mind is nothing other than a mind free from deluded thought.'
(Treatise on No-Mind, 17; T85, no. 2831, p. 1270a15)

'We have to come to a clear understanding as to the true nature and Absolute Existence of Dharma. This truth is that “as all phenomena are strictly dependent, conditioned, and relative, they are therefore impermanent.” This is the Absolute Existence of Dharma. If we have such a penetrative understanding of the nature of phenomena, of the notion of emptiness, we will enter the gateway of Chan, or align ourselves with the Tao. This is what Bodhidharma’s first formula, “facing a wall is the way to pacify the Mind”, teaches us.'
(Gates of Chan (入禅之门), p 33)

Absolute Existence is the translation of 实相 (實相 tattvasya-lakṣaṇam), defined in MMK 18.9:
"To know for oneself, not following others,
Calm extinction, without sophistries,
No differences and no distinctions;
This is termed the 'true character'."
(T30, no. 1564, p. 24a7-8; tr Bocking)

The quote (“缘生无自性、无自性故空”) is from the commentary to MMK 7.17:
'dharmas arising from causal conditions have no self-nature, and having no self-nature are empty'
(T30, no. 1564, p. 10c20-21, tr Bocking)

'But what is this “nature”? If we are to use words and concepts, we can call it the buddha-nature, which is our original nature. This is the nature of awakening, the nature of emptiness or selflessness. Emptiness means relationships, connectedness. Because all things are connected, nothing is fixed, and everything is free.'
(The Essence of Chan by Guo Gu, 1.2)

"But how could one [even] gain the ability to know that it is no-mind [that sees, hears, feels, and knows]?"
"Just try to find out in every detail: What appearance does mind have? And if it can be apprehended: is [what is apprehended] mind or not? Is [mind] inside or outside, or somewhere in between? As long as one looks for mind in these three locations, one's search will end in failure. Indeed, searching it anywhere will end in failure. That's exactly why it is known as no-mind."
(Treatise on No-Mind, 6; T85, no. 2831, p. 1269b9-13)

'it is possible to directly comprehend a thing’s nature and its Absolute Existence, that is, we can know this teacup as the combination of all its necessary conditions. After stripping all those conditions away one by one, we may ask: “Where then is the teacup?” It has no self-identity; it is simply a combination of causative conditions. In this way we can see through to the absolute nature of the thing. Such insight is wisdom. What we observe when looking with such an insight is “suchness” itself, the true actuality, the ultimate truth and Absolute Existence.'
(Gates of Chan, p 146)

'Emptiness is relationships, which means that there is no separation between self and other. Instead of seeing ourselves in the center of everything, we see the connectedness of everything. Selflessness is one of the core teachings that free us from attachments and suffering. It is the realization that all things— including us—are related, that they have no permanent, separate, independent self. This does not mean that we have no personality; we always have one, even after enlightenment. It is not that we do not know our name, or do not recognize anyone, or that our mind is blank—enlightenment is not that at all. What is absent in the enlightenment of selflessness is the fundamental assumption of a permanent, separate, independent self within us and within all things. What we consider as separate, independent, permanent, and solid is actually the coming together of everything else.'
(The Essence of Chan by Guo Gu, 2.4)

'Question. – It is quite possible that the saṃskṛtadharmas, coming from the complex of causes and conditions (hetupratyayasāmagrī), are without intrinsic nature (niḥsvabhāva) and therefore empty (śūnya). But the asaṃskṛtadharmas, which are themselves not dharmas coming from causes and conditions, are indestructible (akṣaya), inalterable (abhedya), eternal (nitya) and like space (ākāśasama). How would they be empty?
Answer. – As I have just said, outside of the saṃskṛtas, there are no asaṃskṛtas, and the true nature (bhūtalakṣaṇa) of the saṃskṛtas is exactly asaṃskṛta. The saṃskṛtas being empty, etc., the asaṃskṛtas themselves also are empty, for the two things are not different.
Besides, some people, hearing about the defects of the saṃskṛtadharmas, become attached (abhiniveśante) to the asaṃskṛtadharmas and, as a result of this attachment, develop fetters.'
(MPPS 48.8; T25, no. 1509, p. 289b5-11)

'All vexations of body and mind are wandering thoughts. Today someone recited a line from the Diamond Sutra, "Not abiding, the mind arises," and asked if it meant having no motivation, or doing nothing. Actually, the line describes the state after enlightenment when wisdom arises and the mind is not attached to anything. When you have motivated yourself to meditate, the will to practice is still a wandering thought. When we are practicing hard, we are still using this false mind (wandering thoughts). On the other hand, true mind is no-mind. How can one practice if there is no-mind?
Everything you do, including meditation, falls under false mind, but if you don't use this false mind to practice, you will never arrive at true mind. The progression of practice is from scattered mind to concentrated mind, from that to unified mind, and from one-mind to no-mind. The first three stages - scattered, concentrated, and unified mind - are all illusory. Only rarely can someone realize no-mind without first going through these three stages.'
(Song of Mind by Sheng-yen, 6.1)

'If you cut off the past and future, and discover that the present does not exist either, at that moment there is no mind. This itself is becoming a Buddha. But if, in the next instant, mind, past, future and present return, then you are again an ordinary sentient being.'
(The Sword of Wisdom by Sheng-yen, online p 187)

'It is not perishable and cannot be praised,
Its substance is like limitless space.
Without leaving where it is, it is constantly clear.
When seeking, you know it cannot be found.
It cannot be grasped, nor can it be discarded;
It is obtained only in the unobtainable.

It is impossible to attain Buddha-nature by grasping for it. Buddha-nature is not something that can be explained or praised. It is as big as empty space and as small as empty space. It contains everything. In the quickest snap of one's fingers every moment of time is present within it. How can one possibly praise something that is beyond comprehension?
No matter where you are, it is possible to perceive Buddha-nature. But the instant you chase after it, it is gone; you will not be able to find it.
Buddha-nature can neither be grasped nor discarded. Only when it is unobtainable can it be obtained. As you can imagine, there is not much one can say about this. So if you cannot attain it, how do you attain it? How can you attain something by not attaining it? In truth, there is no attainment. Buddha-nature is here right from the start.
My question is, "Where is your mind?"
I will tell you something about Buddha-nature: When there is no mind, that is it. But when you put your mind on Buddha-nature, it's gone.'
(The Sword of Wisdom by Sheng-yen, online p 165)