Mbh 12.343.2b

Brahman, desiring to create creatures, caused Agni and Shoma to spring from his own eyes. Afterwards when creatures came to be created, the created persons came out in their due order as Brahmanas and Kshatriyas. He who started into life as Shoma was none else than Brahma; and they that were born as Brahmanas were all Shoma in reality. He who started into being as Kshatriyas were none else than Agni. The Brahmanas became endued with greater energy than the Kshatriyas. If you ask the reason why, the answer is that this superiority of the Brahmanas to the Kshatriyas is an attribute that is manifest to the whole world. It occurred as follows. The Brahmanas represent the eldest creation as regards men. None were created before, that was superior to the Brahmanas. He who offers food into the mouth of a Brahmana is regarded as pouring libations into a blazing fire (for gratifying the deities). I say that having ordained things in comprising this way, the creation of creatures was accomplished by Brahma. Having established all created Beings in their respective positions, he upholds the three worlds. There occurs a declaration to the same effect in the Mantras of the Srutis. Thou, O Agni, art the Hotri in sacrifices, and the benefactor of the universe. Thou art the benefactor of the deities, of men, and of all the worlds. There is (other) authority also for this. Thou art, O Agni, the Hotri of the universe and of sacrifices. Thou art the source through which the deities and men do good to the universe. Agni is truly the Hotri and the performer of sacrifices. Agni is again the Brahma of the sacrifice. No libations can be poured into sacrificial fire without uttering mantras; there can be no penances without a person to perform them; the worship of the deities and men and the Rishis is accomplished by the libations poured with mantras. Hence, O Agni, thou hast been regarded as the Hotri in sacrifices.