Yāska's Nirukta 172.2.3

172.2.3

satyapi tu paryāyavacanatve mukhyataraḥ sambandho madhyamasyendraśabdena, na tathā vāyuvaruṇarudrādibhiḥ | tat kutaḥ ? tathā nigame darśanāt- "sā prathamā saṃsskṛtirviśvavārā sa prathamo varuṇo mitro agniḥ | sa prathamo bṛhaspatiścikitvāṃstasmā3indrāya sutamājuhotaḥ svāhā"-iti | sā prathamā saṃskṛtirityetasmiñchukrāmanthinorhavanamantre yo madhyamo varuṇo'pi mitro'gniḥ, tasmai indrāya sutam ājuhota iti varuṇādīnanukramya viśeṣataścaturthyantena indraśabdena sampradānena sambadhnāti tasmai madhyamāyendrāyeti || tasmāt sampradānena sāmānādhikaraṇyāt mantrānte madhyamaśabdendraśabdayormukhyataraḥ sambandha iti gamyate | yathāsya madhyamasya jyotiṣo mukhyaḥ sambandha indraśabdena, tathetarayorapi pārthivottamayormiksūryaṃśabdābhyām , prasiddhataratvāt sambandhasya | na tathetarairjātavedaḥprabhṛtibhiḥ | sati ca gauṇamukhyatve yuktaṃ yadanyābhidhānena prasiddhatarasambandhena pārthivasya jyotiṣa upadeśaḥ kriyate, na jātavedaḥprabhṛtibhiḥ, tathottamasya sūryaśabdena upadeśaḥ kriyate, na savitṛbhagaprabhṛtibhiriti || kasmāt punarmadhyamasya śabdadvayenopadeśaḥ kriyate, pārthivottamayorekaikena ? iti | madhyamasya hi dvau karmātmānau vidyudvāyvākhyau | tayoranityadarśana eko vidyudākhyaḥ, nitya-