Shatapatha Brahmana 10.5.2.23

10.5.2.23

tadeṣa śloko bhavati anne bhātyapaśrito rasānāṃ saṃkṣare'mṛta iti yadetanmaṇḍalaṃ tapati tadannamatha ya eṣa etasminmaṇḍale puruṣaḥ so'ttā sa etasminnanne'paśrito bhātītyadhidevatam

Now, that man in yonder orb (of the sun), and this man in the right eye, are no other than Death; and he becomes the body (self) of him who knows this: whenever he who knows departs this world he passes into that body, and becomes immortal, for Death is his own self.