Kauṣītaki Upaniṣad 2.5.4

2.5.4

tamukthaśabdābhidheyaṃ ṛgādibuddhyālamvanaṃ etaṃ mukhavinnāntarvartamānaṃ pratyakṣamiva aiṣṭakaṃ iṣṭakāsambandhirūpamaiṣṭakaṃ karmamayaṃ karmasvarūpamātmānamadhvaryuśabdapratyayālambanaṃ adhvaryuṛtvigviśeṣaḥ prāṇabuddhyā saṃskaroti saṃskāraṃ karoti yoṣitamivāgnibuddhyā | ayamarthaḥ yo'yamiṣṭakāsu cito'gniḥ karmasādhanaḥ so'pi prāṇātmaka eva prāṇasya ṛgātmakatvāt, ayañca ṛgādisādhyakarmaniṣpādakaḥ, ahañca tata ṛgātmakaḥ sarvātmā prāṇo 'hamasmi ayamagniśca madātmakaḥ ityātmānaṃ saṃskarotīti | tasmin prāṇabuddhyā saṃskṛte'gnyabhinne ātmani yajurmayaṃ yajuḥsādhyaṃ karmavitānaṃ kuvinda iva pravayati prakarṣeṇa karmamantratantubhirvistārayati | yajurmaye yajuḥsādhye karmavitāne pravṛtte sati ādhārabhūte vā ṛṅmayaṃ ṛksādhyaṃ karmavitānaṃ pravayati hotā ṛtvigviśeṣaḥ | ṛṅmaye ṛksādhye karmaṇi pravṛtte satyādhārabhūte vā sāmamayaṃ sāmasādhyaṃ karmavitānaṃ pravayati udgātā ṛtvigviśeṣaḥ | sa adhvaryuḥ saṃskārahetuḥ prāṇaḥ, eṣa mukhavinnāntaḥsthaḥ sarvasya sarvasyā nikhilāyāstrayīvidyāyāḥ trayī ṛgyajuḥsāmarūpā yā saiva vidyā tasyā ātmā āpyāyaiḥ karttā śarīrasyeva jīvaḥ | uktena prakāreṇa uktamākhyānaṃ sṛṅkhayālikayāha eṣa u eva api mukhavinnāntaḥstha eva na tvanyaḥ, asyātmā asyā