Shatapatha Brahmana · Chapter 10.6.4

aśvāvayaveṣu virāḍavayavopāsanaṃ brāhmaṇam
१०.६.४
uṣā vā aśvasya medhyasya śiraḥ sūryaścakṣurvātaḥ prāṇo vyāttamagnirvaiśvānaraḥ saṃvatsara ātmāśvasya medhyasya dyauṣpṛṣṭhamantarikṣamudaraṃ pṛthivī pājasyaṃ diśaḥ pārśve avāntaradiśaḥ parśava ṛtavo'ṅgāni māsāścārdhamāsāśca parvāṇyahorātrāṇi pratiṣṭhā nakṣatrāṇyasthīni nabho māṃsānyūvadhyaṃ sikatāḥ sindhavo gudā yakṛcca klomānaśca parvatā oṣadhayaśca vanaspatayaśca lomānyudyanpūrvārdho nimlocanjaghanārdho yadvijṛmbhate tadvidyotate yadvidhūnute tatstanayati yanmehati tadvarṣati vāgevāsya vāgaharvā aśvam purastānmahimā'nvajāyata tasya pūrve samudre yonī rātrirenampaścānmahimānvajāyata tasyāpare samudre yoniretau vā aśvaṃ mahimānāvabhitaḥ sambabhūvaturhayo bhūtvā devānavahadvājī gandharvānarvāsurānaśvo manuṣyāntsamudra evāsya bandhuḥ samudro yoniḥ - १०.६.४.