Commentary on the Sūtra of the Collection of the Father and Son (Pitāputrasamāgamanasūtra) (150)

Emptiness without the mark of emptiness is called the signless liberation gate. The dharma of emptiness has no visible, describable, or demonstrable mark; even emptiness itself is empty—this is the signless liberation gate. Knowing that emptiness has no mark whatsoever, that even emptiness does not exist, the mind becomes further liberated. If there is not even the mark of emptiness, not even emptiness itself, what emptiness would there still be to attach to? If there is not even a mark, what should we still seek? There is nothing more to seek at all—this is the wishless liberation gate. Without the mind of aspiration and seeking, the mind becomes even more liberated. When we have accomplished the three liberation gates of emptiness, signlessness, and wishlessness, we are noble ones.

The three dharmas of emptiness, signlessness, and wishlessness practice in accord with emptiness: they neither depart from emptiness, nor do they have the mark of emptiness, and the three are inseparable from one another, progressing layer by layer toward ultimate liberation. If we wish to enter nirvāṇa and attain the unborn and unceasing, we should cultivate in this way, continually producing mental activity of emptiness, becoming ever more empty, until even emptiness itself is empty—only then is the emptying clean and thorough. If there still remains an "emptiness" in the mind, then it is not true emptiness, and the mental activity of emptiness should still be extinguished. One should cultivate and study in this way on the path to nirvāṇa, and thereby realize nirvāṇa. Nirvāṇa is liberation; nirvāṇa is the unborn and unceasing; nirvāṇa is tranquil and unconditioned; nirvāṇa is great freedom and ease.