Shatapatha Brahmana 11.1.2.2

11.1.2.2

taṃ hatvā yajñam agnāveva yonau reto bhūtaṃ siñcatyagnirvai yoniryajñasya sa tataḥ prajāyate taddaśa tā āhutīḥ sampādayedyābhyo vaṣaṭkriyate

And having killed the sacrifice, he pours it, as seed, into the fire as its womb, for, indeed, the fire is the womb of the sacrifice, from out of it it is produced: let him therefore perform those ten oblations for which the Vashat is uttered.