Yāska's Nirukta 25.1.4

25.1.4

ahaḥśabdo hi rātrimahaścobhayamabhidhatte, ataḥ sandehapadam, tasyaiṣa vibhāgo'syāmṛci upapadaviśeṣāt pradarśyate,ahaśca kṛṣṇamiti | bharadvājasyeyamārṣam | triṣṭup | pṛṣṭhasya ṣaṣṭhe'hanyābhimarute śastre śasyate | "ahaśca kṛṣṇaṃ rātriḥ śuklaṃ cāharjunam” | arjunaśabdo hi śuklaparyāyaḥ | “vivarttate” viparyyayeṇa varttate | rātriratītā, aha̍r āyātam, aharatītaṃ, rātrirāyātā, ityevam | "rajasī” rañjake | jyotiṣā hi bhūtānyaho rañjayati, tamasā rātriḥ | "vedyābhiḥ” “veditavyābhiḥ pravṛttibhiḥ” na hi tāsāṃ pravṛttīnāmanto'sti, ahani ca rātrau ca prāṇinām | atastā veditavyā eva bhavanti, bahutvāt, na hi viditānāmantaḥ kadācit | kiñca, “vaiśvānaraḥ” agniḥ “avātirat” “avāhan” apahanti, svena "jyotiṣā tamāṃsi” || kathaṃ punarapahanti?, “jāyamāno na rājā” “jāyamāna iva” "udyan” “sarveṣāṃ” sarvabhūtānāṃ “rājā” “ādityaḥ” | yathā hyudyannādityastamāṃsi apahanti divā, evam “agniḥ” api rātrāvapahantītyagnirādityena tama upaghātaṃ pratyupamīyate | 21 | ( atha meghanāmanirvacanam )