Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.2.22

3.2.2.22

athāgnaye paridāya svapiti | devānvā eṣa upāvartate yo dīkṣate sa devatānāmeko bhavati na vai devāḥ svapantyanavaruddho vā etasyāsvapno bhavatyagnirvai devānāṃ vratapatistasmā evaitatparidāya svapityagne tvaṃ su jāgṛhi vayaṃ su mandiṣīmahītyagne tvaṃ jāgṛhi vayaṃ svapsyāma ityevaitadāha rakṣā ṇo aprayucanniti gopāya no 'pramatta ityevaitadāha prabudhe naḥ punaskṛdhīti yathetaḥ suptvā svasti prabudhyāmahā evaṃ naḥ kurvityevaitadāha

He then gives himself up to Agni (the fire) for protection and lies down to sleep. For he who is consecrated draws nigh to the gods and becomes one of the deities; but the gods do not sleep, while to him sleeplessness is not vouchsafed; and Agni being Lord of vows to the gods, it is to him that he now commits himself and lies down to sleep, with the text (Vâg. S. IV, 14), 'O Agni, be thou a good waker: may we thoroughly refresh ourselves!' whereby he says, 'O Agni, wake thou: we are going to sleep!'--'Guard us unremittingly!' whereby he means to say, 'protect us heedfully!'--'Make us awake again!' whereby he means to say, 'Order so that, having rested here, we may awake safely.'