Kaṭha Upaniṣad 3.12

3.12

eṣa indriyādikāryavargātparatvenoktaḥ ātmā pratyakcaitanyarūpaḥ sarveṣu brahmādistambānteṣu bhūteṣu prāṇiṣu sthito'pi gūḍhaḥ avidyayā ācchāditaḥ san na prakāśate sarvasmātpara ānandarūpo'hamiti vyavahārayogyo na bhavatītyarthaḥ | nanu tamkratuḥ paśyati vītaśoka iti pūrvoktādviruddhaṃ na prakāśate iti kathamucyate ityāśaṃkya cittaśuddhacaśuddhibhyāmadhikāribhedānna virodha ityāha-dṛśyatetviti| tu śabdaḥ | evārthakaḥ | sūkṣmadarśībhiḥ indriyebhyaḥ parā hyarthā ityādi prakāreṇottarottarasūkṣmatvavicāreṇa sūkṣmātmatattvaṃ draṣṭuṃ śīlaṃ yeṣāṃ taiḥ paṇḍitaiḥ agryayā mukhyayā gurūpadiṣṭamahāvākyajanyayā sūkṣmayā sūkṣmapadārthagrahaṇasamarthayā buddhyā niścayātmikayaiva eṣaḥ ātmā dṛśyate pratyagrūpeṇa sākṣātkriyata ityarthaḥ |
buddhyaikāgryaṃ vinā sūkṣmatattvasya bhānāsaṃbhavāttadekāgryaprakāramāha-