Śatapatha Brāhmaṇa ("of a hundred paths") 11.3.3.1

11.3.3.1

brahma vai mṛtyave prajāḥ prāyacat tasmai brahmacāriṇameva na prāyacatso'bravīdastu mahyamapyetasminbhāga iti yāmeva rātriṃ samidhaṃ nāharātā iti tasmādyāṃ rātrim brahmacārī samidhaṃ nāharatyāyuṣa eva tāmavadāya vasati tasmādbrahmacārī samidhamāharennedāyuṣo'vadāya vasānīti

The Brahman delivered the creatures over to Death, the Brahmakârin (religious student) alone it did not deliver over to him. He (Death) said, 'Let me have a share in this one also.'--'Only the night on which he shall not bring his fire-wood,' said (the Brahman). On whatever night, therefore, the Brahmakârin does not bring fire-wood, that (night) he passes cutting it off from his own life: therefore the Brahmakârin should bring fire-wood, lest he should pass (his nights) cutting off (as much) from his life.