Shatapatha Brahmana 14.3.1.7

14.3.1.7

atha tṛtīyamabhyādhāya tasminnāsīno juhotyadha-iva vai tadyadāsīno'dha-iva tadyadayaṃ lokastadyemaṃ lokaṃ śugāviśattayaivainametacucā samardhayati kṛtsnaṃ karoti

Then, having put the third (bundle) on the fire, he offers on it whilst sitting; for below, as it were, is he who is sitting; and below, as it were, is this (terrestrial) world: thus the thereby supplies and completes it with that heat which had entered this (terrestrial) world.