Yāska's Nirukta 168.1

168.1

tadyathainānyudāharaṇāni ānupūrvyeṇaiva saptasvapi vibhaktiṣu indro diva ityevamādīni,— “indro̍ di̱va indra̍ īśe pṛthi̱vyā indro̍ a̱pāmindra̱ itparva̍tānām | indro̍ vṛ̱dhāmindra̱ inmedhi̍rāṇāmindraḥ kṣeme̱ yoge̍ havya̱ indra̍ḥ || ( ṛ0 saṃ0 8, 4, 15, 5 )”—iti || reṇorvaiśvāmitrasyeyamārṣam | aindrī | triṣṭup | sūryastutyekāhe niṣkevalye viniyuktā || “indro divaḥ” “īśe” īṣṭe | “indraḥ” eva “pṛthivyāḥ” īṣṭe | ‘indraḥ’ eva ‘apām’ īṣṭe varṣakarmādinā | ‘indraḥ’ eva ‘parvatānāṃ’ meghānām īṣṭe | ‘indraḥ’ eva ‘vṛdhām’ atipravṛddhānāmapi bhūtānāmīṣṭe | ‘indraḥ’ eva ca ‘madhirāṇāṃ’ yajñaistadvatāmīṣṭe | ‘indraḥ’ eva hi ‘yoge’ aprāptalābhe prāptavye, ‘kṣeme’ ca paripālane karttavye ‘havyaḥ’ āhvātavyaḥ | nānyaḥ kaścitsamartha etatkarttumityabhiprāyaḥ | prathamāyāmetadudāharaṇam | “indra”-ityetasmādupapadāt ‘īśe’-ityeṣaprathamapuruṣa iti pratīyate, nottamapuruṣa iti ||