Śatapatha Brāhmaṇa ("of a hundred paths") 2.3.3.7

2.3.3.7

tadvā eṣa eva mṛtyuḥ | sa eṣa tapati tadyadeṣa eva mṛtyustasmādyā etasmādarvācyaḥ prajāstā mriyante 'tha yāḥ parācyaste devāstasmādu te 'mṛtāstasyemāḥ sarvāḥ prajā raśmibhiḥ prāṇeṣvabhihitāstasmādu raśmayaḥ prāṇānabhyavatāyante

Now yonder burning (sun) doubtless is no other than Death; and because he is Death, therefore the creatures that are on this side of him die. But those that are on the other side of him are the gods, and they are therefore immortal. It is by the rays (or reins, thongs, rasmi) of that (sun) that all these creatures are attached to the vital airs (breaths or life), and therefore the rays extend down to the vital airs.