Yāska's Nirukta 7.1.1

7.1.1

“ṛcāṃ tvaḥ (ṛ0 saṃ0 8, 2, 24, 5)”—iti | bṛhaspaterārṣam || ṛtvikkarmaṇāṃ viniyogamanayarcā''caṣṭe-“ṛcāṃ tvaḥ poṣam” iti | ya ete catvāro mahartvijaḥ, eteṣāṃ ‘tvaḥ’ eka ityarthaḥ | kimekaḥ karoti ? ‘ṛcāṃ’ ‘poṣaṃḥ’ puṣṭiṃ ‘pupuṣvān’ punaḥ punaḥ bhṛśaṃ vā devatāyāthātmyānucintanasantānagarbhasthānakaraṇānupradānavatīryathākālamṛco'dhīyānaḥ ‘āste’—sa hi tāsāṃ poṣaḥ | katamaḥ ?, ‘ekaḥ’ etatkarma kurvannāste iti,— ‘hotā’ etattāvadṛgadhyayanakarma tasmin hotari viniyuktam, uktaṃ ca—“yadṛcaiva hautraṃ kriyate”—iti ( ai0 brā0 5, 5, 8) | ‘gāyatraṃ tvaḥ’ 1 gāyatrameko. ‘gāyati’ ‘śakvarīṣu’ ṛkṣu | katamaḥ ?, ‘udgātā’ tasminnapyetatsāmagānakarma viniyuktam, uktaṃ ca- "sāmnodrotham"-iti (ai0 brā0 5, 5, 8) "brahmā tvaḥ" brahmā nāma eka ṛtvik 'jāte' prāyaścitte 'vidyāṃ vadati' | vidyātrayahetutvādātmano vidyāṃ vijñānaṃ vadatītarebhya ṛtvigbhyaḥ-idamatra kuruteti | tatrāpi hyetat karma viniyuktam | sa punareṣa sarvavidyaḥ sarvavijñānamanthāvidhau hyasāvadhikārī trayīvidyāsaṃyukto yenāsau sarvameva veditumarhati | na hyasarvavit tamadhikāraṃ śaknuyānnirvarttayitum | uktaṃ ca- "atha kena brahmatvaṃ kriyata iti? trayyāvidyayā"-iti ( ai0 brā0 5, 5, 8)|| "yajñasya mātrāṃ vimitīta u tvaḥ |" vimimīta eka iti | mīyata iti mānaṃ karma, tanmātretyucyate | yā kāciditikarttavyatā yajñasya, tāṃ vimimīte'dhvaryuḥ, nānāprakāraṃ karotītyarthaḥ ||