Śatapatha Brāhmaṇa ("of a hundred paths") 8.6.3.6

8.6.3.6

yadveva gārhapatyamupadadhāti | vedirvai devaloko 'tha vā eṣa bahirvedi cito bhavati taṃ yadihāhṛtyopadadhāti tadenaṃ vedau devaloke pratiṣṭhāpayati

And, again, as to why he lays down the Gârhapatya. The world of the gods, doubtless, is the Vedi (altar-ground); but that (original Gârhapatya) is built up outside the Vedi: thus, when he brings it here and lays it down (on the fire-altar), he then establishes it (or him, Agni) on the Vedi, in the world of the gods.