Śatapatha Brāhmaṇa ("of a hundred paths") 8.6.3.7

8.6.3.7

yadveva gārhapatyamupadadhāti | yonirvai puṣkaraparṇamatha vā eṣa bahiryoni cito bhavati bahirdho vā etadyoneragnikarma yatpurā puṣkaraparṇāttaṃ yadihāhṛtyopadadhāti tadenaṃ yonau puṣkaraparṇe pratiṣṭhāpayati tatho haiṣo 'bahirdhā bhavatyaṣṭāviṣṭakā upadadhāti tasyokto bandhustaṃ vā etaireva yajurbhiretayāvṛtā cinoti yo hyevāsau sa evāyaṃ tamevaitadāhṛtyehopadadhāti

And, again, as to why he lays down the Gârhapatya. The lotus-leaf, doubtless, is a womb, but that (Gârhapatya) is built up outside the womb, and outside of the womb indeed takes place that performance regarding the fire-altar which takes place prior to the (laying down of the) lotus-leaf: thus, when they bring it (the Gârhapatya) here and lay it down, he then establishes it in the womb. on the lotus-leaf; and thus indeed it is not outside. Eight bricks he lays down: the significance of this has been explained. He builds it up with the same formulas and in the same order, for this one is the same as that (former Gârhapatya Agni) he thus brings it (or him) here and lays it down.