Śatapatha Brāhmaṇa ("of a hundred paths") 3.1.1.7

3.1.1.7

tasmādu ha na pratīcīnaśirāḥ śayīta | neddevānabhiprasārya śayā iti yā dakṣiṇā dik sā pitṝṇāṃ yā pratīcī sāsarpāṇāṃ yato devā uccakramuḥ saiṣāhīnā yodīcī dik sā manuṣyāṇāṃ tasmānmānuṣa udīcīnavaṃśāmeva śālāṃ vā vimitaṃ vā minvantyudīcī hi manuṣyāṇāṃ digdīkṣitasyaiva prācīnavaṃśā nādīkṣitasya

For this reason one mug not sleep with his head towards the west, lest he should sleep stretching (his legs) towards the gods. The southern quarter belongs to the Fathers; and the western one to the snakes; and that faultless one is the one where the gods ascended (to heaven); and the northern quarter belongs to men. Hence in human (practice) a hall or shed is constructed with the top-beams running from south to north, because the north is the quarter of men. It is only for a consecrated, not for an unconsecrated person that it is (constructed) with the top-beams running from west to east.