Excerpt from the Sutra of Perfect Enlightenment

Original text: 善男子。云何我相。谓诸众生心所证者。善男子。譬如有人。百骸调适。忽忘我身。四支弦缓。摄养乖方。微加针艾。则知有我。是故证取。方现我体。善男子。其心乃至。证于如来。毕竟了知。清净涅槃。皆是我相。

Explanation: The Buddha said: "Sons of goodness, what is the mark of self? What are the manifestations and characteristics of the mark of self? The mark of self is that aspect which can be realized and known by the consciousness mind of sentient beings — the aspect that can perceive. Sons of goodness, it is like a person whose entire body — every joint, muscle, tendon, and vessel — feels extremely comfortable, without any discomfort or disharmony whatsoever; as a result, this person forgets the existence of the material body, and there is no sensation of the body in the mind. The four limbs are completely relaxed, and he does not even know where his body is; there is no information or thought concerning the body. At this moment, if a fine needle is gently pricked into his body, he immediately becomes aware of the existence of his body, and thus realizes the self — the concept of 'my body' appears. Sons of goodness, even if the mind realizes the Tathāgata and can ultimately and thoroughly know the pure nirvāṇa, all of this is still the mark of self."

What the Buddha said in this passage shows that the mark of self is very subtle. The coarse mark of self can be realized and also eradicated by arhats, but the extremely subtle mark of self can only be realized and eradicated when one has cultivated to the stage of a bodhisattva who has attained the bhūmis. The mark of self here refers to sentient beings' extremely subtle knowing nature regarding themselves and all dharmas. As long as there is a knowing — no matter what is known, no matter how subtle what is known is, no matter how fine the knowing is — it is the mark of self; without a self, there is no knowing. Recognizing and accepting this knowing nature is the view of self (satkāya-dṛṣṭi); grasping this knowing nature is self-grasping, which can also be called dharma-grasping — dharma-grasping is the subtle self-grasping. Having recognized and accepted this knowing nature is ignorance; there will then be karmic formations, and there will be transformational birth-and-death (parināma-maraṇa), and one cannot attain ultimate nirvāṇa.

If sentient beings say, "I have realized the fruit," and recognize and grasp the mind-state that realizes the fruit — this realizing nature — that is the mark of self, that is the view of self. If someone says, "I am enlightened," and recognizes and grasps this mind-state capable of enlightenment, that is the self-mind, that is the view of self. If sentient beings believe that they are good, that they are the best, while others are bad, that others are the worst, then there is the mark of self, which is the view of self. With this view of self, one will create karma of birth-and-death, and there will be segmented birth-and-death (pariccheda-maraṇa) and transformational birth-and-death (parināma-maraṇa), and one cannot attain liberation and nirvāṇa. If someone considers himself superior to others and constantly exalts himself while belittling others, this is a serious mark of self, a coarse mark of self; the karma of birth-and-death is heavy, and the three evil destinies cannot be avoided. If someone goes to great lengths to cover up his own shortcomings and weaknesses, that is a serious mark of self. If someone goes to great lengths to expose and attack others, that is likewise a serious mark of self. Both are coarse and heavy marks of self; the view of self is heavy, and the three evil destinies cannot be avoided.

All bodily formations, verbal formations, and mental formations are the mark of self. If one does not recognize, accept, and grasp them, there is no view of self; if one recognizes, accepts, and grasps them, that is the view of self and self-grasping. The behavior of shielding one's own faults and of fighting and contending is having the mark of self. The various expressions on the face are the mark of self — for example, embarrassment, blushing, awkwardness, shyness, joy, anger, and hostility all involve the mark of self. All evil and unwholesome actions contain the mark of self, and the wholesome actions of most sentient beings also contain the mark of self. The wholesome actions of the sages occur naturally and spontaneously, without the mark of self. In all of the Buddha's bodily, verbal, and mental actions, there is no mark of self.