Zekkai Chūshin (1336-1405), considered to be the dominant poet of all the Five Mountains Zen Poet-monks, once referred to Tsung-mi as “the old man in the nāga [mythological serpent = the Buddha] samadhi.” (Broughton, ZOC) The origin of this can be traced back to the Platform Sutra of Huineng:
“Mirror-like Wisdom is pure by nature;
Wisdom that comprehends all things equally, frees the mind from all impediments;
All-discerning Wisdom sees things intuitively;
All-performing Wisdom, like Mirror-Wisdom, is free from prejudice.
Perception-consciousness of the five-sense-vijnanas,
And the Universal Consciousness of the Alaya-vijnana,
Are not ‘transmuted’ to Prajna, until the Buddha-stage;
While the intellective-consciousness of the Manas,
And the discriminative-consciousness of the Manovijnana,
Are ‘transmitted’ in the Bodhisattva-stage.
When you are able to free yourself entirely from attachments to sense-objects as these ‘transmutations’ take place,
Then you will forever abide in the never-ceasing Naga Samadhi.”
When one is able to transcend the skandhic-matrix, one is thereby empowered to forever dwell in the Nāga Concentration—meaning to focus on that “primordial turning point” wherein all designs of the body consciousness (combined Alaya-Manas configurations) are rendered still-bound by the Dragon Eye of Tathata ( the Divine and Noble Wisdom Eye of all Tathagatas). The Nāga-Samadhi is truly an inconceivable state. As the Platform Sutra states, this concentration is an “all discerning” Wisdom—because it is perfectly mirrored from the Noble-Wisdom of the Tathagatas. The earliest protectors of this Wisdom are the ancient Nāgas; the Chinese equivalents of the nāgas are the dragons and their early symbolism runs thus:
In China it was believed that pearls were formed from the mouth of the ocean dragon, whilst in India it was believed that they were produced by the fire of the sun. It was an Indian belief that pearls protected against harm from fire. A pair of Chinese dragons are often represented as fighting for possession of the flaming pearl, or chasing the elusive pearl across the skies. Momentary contact of the dragon with the flaming pearl produces the lightning flash which illuminates the darkness of the black clouds, revealing the brilliant zigzag form of the dragon as white lightning and the rolling roar of his voice as the crashing of thunder. The flaming pearl is in essence the egg of potentiality which is fertilized by the dragon. As a polarity symbol it is the negative point or seed-essence which comes into contact with a positive charge during an electrical storm. Its rapid movement across the skies is traced in the flicker of lightning and its forked ascent and descent to earth. One form of lightning is actually known as ‘pearl lightning’, where the fork tip explodes into a multitude of small white spheres. The flaming pearl has been identified as ball lightning, the sun, the moon, the essence of dragon seed, and ‘the pearl of great price’ as the Buddhist wish-fulfilling gem. (Robert Beer: Encyclopedia of Tibetan Symbols and Motifs, pg. 65)
Formerly it was the nāgas, like Nāga Kanya, who guarded the wish-fulfilling jewel in the mystical conch-shell. Of course, within Mystical-Buddhism the ‘pearl of great price’ is the beloved “Bodhi-Pearl of Noble Wisdom.” Hence, this Wisdom is Inconceivable. Which is the perfect description of a Mystical Black Dragon—those filled with that Inconceivable Wisdom; without question Tsung-mi is amongst them.
One of the Sutras that Tsung-mi frequently makes reference to in the Chan Prolegomenon is the Heroic Progress Samadhi Sutra. Like the Sutra of Perfect Enlightenment, it is based on the Sudden Awakening-Gradual Cultivation Model:
As the [Heroic Progess Samadhi] Sutra says: “As to principle, one all-at-once awakens; riding this awakening, [thoughts of the unreal] are merged into annulment. But phenomena are not all-at-once removed; [only] by a graduated sequence are they exhausted.”139 Therefore, Guifeng [Zongmi] deeply clarified the principle of first awakening and later practice [sŏno husu]…. As to sudden awakening [tono], when the ordinary being is deluded, [he assumes that] the four elements are his body and thought of the unreal is his mind. He is unaware that his self nature is the true dharma body. He is unaware that his own empty Knowing [hŏji] is the the true Buddha. He seeks the Buddha outside mind and is on a constant run. Suddenly entrance to the road is pointed out to him by a good guide. For one moment he retraces the light and sees his own self nature. The ground of this nature from the outset is free of the depravities; [it is] the no-outflows knowledge nature complete from the outset, not the slightest bit different from all the buddhas. Therefore, we speak of sudden awakening. As for gradual practice [chŏmsu], having suddenly awakened to the realization that the original nature is no different from the buddhas, the beginningless habit energy is difficult to eliminate finally, and, therefore, he relies on this awakening to practice. The results of this gradual perfuming mature, nourishing the sagely embryo. After a long time, he becomes a noble one, and, therefore, we speak of gradual practice.
Broughton, Jeffrey Lyle (2012-08-14). Zongmi on Chan (Translations from the Asian Classics) (Kindle Locations 1664-1672). Columbia University Press. Kindle Edition.
A more familiar name for this sutra is the Sūraṅgama Samādhi Sūtra. This is a premier text for Bodhisattva-advancement. This describes a most profound Samādhi-state. It is only attainable “by Buddhas and 10th Level Bodhisattvas.”
Others of the 100 ‘miracles’ which this samadhi empowers its possessor to perform include being able to change sex at will; placing immense Buddha Paradises (universes) into a single pore of the skin; always presiding over the superknowledges (abhijna); always emitting rays of light over all universes without exception; being able to speak and understand all languages of all universes; and possessing a knowledge which is profound and unfathomable.Part of that knowledge is that all dharmas (things) have their basis in the dharma-dhatu – the Totality of all that is, the All. In this sense, there is non-duality that characterises everything, since everything is possessed of the ‘one flavour’ of the dharma-dhatu.
One can well understand why it was a favorite of Tsung-mi, and why it had a dominant role in the development of his Chan Prolegomenon.