Maitri (Maitrāyaṇīya) Upaniṣad 6.20

6.20

athānyatrāpyuktam ataḥ parāsya dhāraṇā tālurasanāgranipīḍanā-dvāṅmanaḥprāṇanirodhanādbrahma tarkeṇa paśyati yadātmanā''tmāna-maṇoraṇīyāṃsaṃ dyotamānaṃ manaḥkṣayātpaśyati tadātmanātmānaṃ dṛṣṭvā nirātmā bhavati nirātmakatvādasaṅkhyo'yoniścintyo mokṣalakṣaṇamityetatparaṃ rahasyam ityevaṃ hyāha
cittasya hi prasādena hanti karma śubhāśubham |
prasannātmātmani sthitvā sukhamavyayamaśnutā iti ||

20. Now, it has elsewhere been said: ‘One may have a higher concentration than this. By pressing the tip of his tongue against the palate, by restraining voice, mind, and breath, one sees Brahma through contemplation.’ When through self, by the suppressing of the mind, one sees the brilliant Self which is more subtile than the subtile, then having seen the Self through one’s self, one becomes self-less (nir-ātman). Because of being selfless, he is to be regarded as incalculable (a-saṅkhya), without origin—the mark of liberation (mokṣa). This is the supreme secret doctrine (rahasya). For thus has it been said:—

For by tranquillity (prasāda) of thought
Deeds (karman), good and evil, one destroys!
With soul (ātman) serene, stayed on the Soul (Ātman),
Delight eternal one enjoys!