Śatapatha Brāhmaṇa ("of a hundred paths") 8.6.3.14

8.6.3.14

taddhaike | jaghanārdhe gārhapatyamupadadhati pūrvārdhe punaścitimāhavanīyaśca vā etau gārhapatyaścaivaṃ vā etāvagnī iti na tathā kuryādayaṃ vai loko gārhapatyo dyaurāhavanīya uttaro vā asāvasyai tasmādenāmuttarāmevopadadhyāt

Now some lay down the Gârhapatya on the hind part, and the Punaskiti on the front part (of the built altar), for these two are the Âhavanîya and the Gârhapatya, and these two fires are (placed) in this way. Let him not do this, for the Gârhapatya is this (terrestrial) world, and the Âhavanîya is the sky; and above this (earth) surely is yonder (sky); let him therefore place it (the Punaskiti) on the top of that (Gârhapatya).