Śatapatha Brāhmaṇa ("of a hundred paths") 2.1.4.7

2.1.4.7

atha jāgrati devāḥ | taddevānevaitadupāvartate sa sadevataraḥ śrāntatarastapasvitaro 'gnī ādhatte tadvapi kāmameva svapyānno hyanāhitāgnervratacaryāsti mānuṣo hyevaiṣa tāvadbhavati yāvadanāhitāgnistasmādvapi kāmameva svapyāt

Thereupon they remain awake (during that night). The gods are awake: so that he thereby draws nigh to the gods, and sets up his fires as one more godly, more subdued, more endowed with holy fervour (tapas). He may, however, sleep, if he choose, since the observance of the vow is not necessary for him who has not performed Agnyâdheya. For so long as he has not set up a (sacrificial) fire of his own, he is a mere man; and he may, therefore, sleep, if he choose.