Shatapatha Brahmana 8.7.1.18

8.7.1.18

atha prathamāyai svayamātṛṇāyai | upariṣṭādviśvajyotiṣamupadadhātīyaṃ vai prathamā svayamātṛṇāgniḥ prathamā viśvajyotiritastadūrdhvamagniṃ dadhāti tasmādita ūrdhvo 'gnirdīpyate 'tho prajananametaditastadūrdhvam prajananaṃ dadhāti tasmādita ūrdhvameva prajāyate

Now the (first) Visvagyotis he lays down subsequent to the first naturally-perforated one; for the first naturally-perforated one is this (earth), and the first Visvagyotis is Agni: he thus sets up Agni upwards from this (earth), whence the fire blazes upwards from here. But there also is generative power therein: he thus places generative power above this (earth), whence procreation only takes place above this (earth).