The Śūraṅgama Sūtra, Volume Five: The Twenty-Five Sages' Dharma Gates of Perfect Penetration — Upaniṣada

Original text:优波尼沙陀。即从座起。顶礼佛足。而白佛言。我亦观佛最初成道。观不净相。生大厌离。悟诸色性。以从不净。白骨微尘。归于虚空。空色二无。成无学道。如来印我。名尼沙陀。尘色既尽。妙色密圆。我从色相。得阿罗汉。佛问圆通。如我所证。色因为上。

Explanation: Upaniṣada immediately rose from his seat, bowed at the Buddha's feet, and said to the Buddha: I also observed that after the Buddha first attained the Way, he taught the Dharma to the bhikṣus. I chose to cultivate the white-bone contemplation, contemplating the impurity of the material body, and there arose in my mind a great sense of revulsion toward the material body. I awakened to the nature of all material form: it proceeds from impurity—the white bones reduced to fine dust, gradually returning to empty space. I awakened to the fact that both emptiness and form are nonexistent, and I accomplished the stage beyond training (aśaikṣa), the fourth fruit. The Tathāgata certified me and named me Niṣada (subtle form). When the contemplative practice reached its end and the forms of the six sense objects were exhausted within the mind, the wondrous form contained profound and hidden completeness. I attained arhatship through the mark of form. The Buddha asked me about the method of perfect penetration; as I myself realized it, contemplating the impurity of the material body is the most fundamental.

Upaniṣada cultivated the white-bone contemplation, contemplating the impurity of the material body, visualizing the material body as white bones, then visualizing the white bones as subtle material sense-objects, and finally the subtle material sense-objects vanished and became empty nothingness. All of this contemplative practice was carried out within profound meditative concentration (dhyāna). The white bones manifested through this contemplative practice belong to the form of meditative fruit (dhyāna-fruit form), invisible to others; only the practitioner himself can see it with the wisdom eye within meditative concentration. This seeing is not seeing with the fleshy eye; otherwise, others would be able to see it as well. After he saw the white bones in meditation, he continued his contemplative practice, visualizing the white bones as the finest dust particles, approaching the particles of empty space, and finally they transformed into nothingness. In his mind, there was neither form nor emptiness—everything was completely empty. These states all belong to the form of meditative fruit; they are states of meditative absorption (samādhi), possessing both concentration and wisdom. Relying on this state of samādhi, one can attain liberation from the three realms.

If one lacks meditative concentration and yet attempts to contemplate these dharmas, one can only imagine them with the mind consciousness, but one will never be able to imagine the white bones and fine dust particles, let alone transform the dust particles into emptiness and then empty the emptiness itself. Therefore, the equal cultivation of samādhi and prajñā is called genuine practice, and the result of genuine practice is called genuine realization. The cultivation and realization of all dharmas are like this; there is no other shortcut. Meditative concentration cannot be avoided or bypassed.