Shatapatha Brahmana 9.2.1.20

9.2.1.20

agnau tvevotsādayet | ime vai lokā eṣo 'gnirāpaḥ pariśritastaṃ yadagnā utsādayati tadevainam pariṣyanda utsādayati

But let him rather set it out on the fire-altar;--for that fire-altar is these worlds, and the enclosing-stones are the waters;--so that when he sets it out on the fire-altar, he indeed sets it out on an island.