Yāska's Nirukta 50.2.8

50.2.8

āha-doḥ kasmāt ? ucyate-“doḥ” “dravateḥ” ( bhū0 pa0) | tasya hi prāṇena paśurdravīti | śritamaṃbhāvena etatkāryye bhavatīti śitāma | yadā dorviṣaye śitāmaśabdaḥ tadaivaṃ nirvaktavyaḥ || āha-kayopapattyā doḥ śitāmaśabdenocyate ? śṛṇu-paśorhi bāhyāni cāvadānāni, ābhyantarāṇi ca bhavantīti | tatra, paśoḥ pārśve śroṇyāvaṃsāviti bāhyāni, jihvāhṛdyakṛdādīni ābhyantarāṇi | tatraivaṃ sati pārśvataḥ śroṇitaḥ-ityetayorbāhyayorantarā varttamānaḥ śitāmaśabdaḥ kimanyaddoṣṇo'bhidadhyāt| prāyo'pi hi niyamako bhavati| evaṃ bāhyāvadānaprāye ca śitāmaśabdo varttate iti dorviṣayaḥ kalpyate || “yoniḥ śitāmaḥ”-“iti” “śākapūṇiḥ” ācāryo manyate | tatra yoniḥ anavadānīyā eva | yonisamānadeśastu gudo nāmāvadānamasti, sa yoniśabdenocyate | sa ca gudaḥ “viṣito bhavati” | ‘viṣḷ vyāptau’ ( ju0 u0 ), vyāptaḥ sa purīṣeṇa bhavati | athavā viṣitamāṃso vipuṣitamāṃsaḥ, vikṣiptamāṃsaḥ, sa bhavati | āha-kayopapattyā śākapūṇirmate yoniḥ śitāmaśabdenocyate ? iti | śṛṇu-sa hi śroṇya- nantaro bhavati, śroṣyanantaraṃ ca śitāmaśabda ucyate, -śroṇitaḥ śitāmata iti | śabdasārūpyamapi ca kiñcidasti, -viṣikto bhavati, śitāmeti | anayopapatyā anena ca śabdasārūpyena yoniḥ śitāma iti śākapūṇirmanyate || "śyāmatau yakṛtaḥ"- "iti" "taiṭikiḥ" ācāryo manyate || yaduktaṃ bhavati śyāmata iti, taduktaṃ bhavati śitāmata iti | evaṃ hi bahutaraṃ śabdasārūpyaṃ lakṣyate evaṃ ca sati yakṛta etadavadānaṃ coditaṃ syāditi gamyate || kiṃ kāraṇam ? taddhi "śyāmaṃ" "śyāyateḥ" ( bhū0 ā0 ) dhātoḥ, taddhi samparkādupapadyate ||