Shatapatha Brahmana 10.6.5.8

10.6.5.8

tamanavarudhyevāmanyata taṃ saṃvatsarasya parastādātmana ālabhata paśūndevatābhyaḥ pratyauhattasam:tsarvadevatyam prokṣitam prājāpatyamālabhanta eṣa vā aśvamedho ya eṣa tapati tasya saṃvatsara ātmāyamagnirarkastasyeme lokā ātmānastāvetāvarkāmedhau so punarekaiva devatā bhavati mṛtyurevāpa punarmṛtyuṃ jayati nainam mṛtyurāpnoti mṛtyurasyātmā bhavati sarvamāyuretyetāsāṃ devatānāmeko bhavati ya evaṃ veda

He bethought him of leaving it unrestrained. At the end of a year he slaughtered it for his own self, and made over the (sacrificial) animals to the deities: therefore they slaughter the consecrated (victim) as one that, in its nature as Pragâpati, represents all the deities. But the Asvamedha, in truth, is he that shines yonder (the sun), and the year is his body. The Arka is this Fire, and these worlds are his bodies. These two are the Arka and Asvamedha; but these, indeed, become again one deity, to wit, Death. And, verily, whosoever knows this, conquers recurrent Death, and Death has no hold on him: Death is his own self; he attains all life, and becomes one of those deities.