Brihadaranyaka Upanishad (with commentary) · Chapter 5.15

BrhUpBh_5,14.8 gāyatryā mukhavidhānāyārthavāda ucyate-etaddha kila vai smaryate /
tattatra gāyatrīvijñānaviṣaye janako vaideho buḍilo nāmato 'śvatarāśvasyāpatyamāśvatarāśvistaṃ kiloktavān /
yannu iti vitarke ho aho ityetattadyattvaṃ gāyatrīvidbrūthā gāyatrīvidasmīti yadabrūthāḥ kimidaṃ tasya vacaso 'nanurūpam /
atha kathaṃ yadi gāyatrīvitpratigrahadoṣeṇa hastobhūto vahasīti /
sa pratyāha rājñā smārito mukhaṃ gāyatryā hi yasmādasyā he samrāṇna vidāñcakāra na vijñātavānasmīti hovāca /
ekāhgavikalatvādgāyatrīvijñānaṃ mamāphalaṃ jātam /
śṛṇu tarhi tasyā gāyatryā agnireva mukham /
yadi ha vā api bahvivendhanamagnāvabhyādadhati laukikāḥ sarvameva tatsaṃdahatyevendhanamagnirevaṃ haivaivaṃvidgāyatryā agnirmukhamityevaṃ vettītyevaṃvitsyātsvayaṃ gāyatryātmāgnimukhaḥ san /
yadyapi bahviva pāpaṃ kurute pratigrahādidoṣaṃ tatsarvaṃ pāpajātaṃ saṃpsāya bhakṣayitvā śuddho 'gnivatpūtaśca tasmātpratigrahadoṣādgāyatryātmājaro 'mṛtaśca saṃbhavati //8//
iti śrīmadbṛhadāraṇyakopaniṣadbhāṣye pañcamādhyāyasya caturdaśaṃ brāhmaṇam //14//
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hiraṇmayena pātreṇa satyasyāpihitaṃ mukham |
tat tvam pūṣann apāvṛṇu satyadharmāya dṛṣṭaye |
pūṣann ekarṣe yama sūrya prājāpatya vyūha raśmīn samūha tejaḥ |
yat te rūpaṃ kalyāṇatamam tat te paśyāmi yo 'sāv asau puruṣaḥ so 'ham asmi |
vāyur anilam amṛtam athedaṃ bhasmāntaṃ śarīram |
oṃ krato smara kṛtaṃ smara krato smara kṛtaṃ smara |
agne naya supathā rāye 'smān viśvāni deva vayunāni vidvān |
yuyodhy asmaj juhurāṇam eno bhūyiṣṭhāṃ te namauktiṃ vidhema