Śatapatha Brāhmaṇa ("of a hundred paths") 2.4.4.25

2.4.4.25

tadvai pañcaiva bhakṣayanti | hotā cādhvaryuśca brahmā cāgnīcca yajamānaḥ pañca vā ṛtavastadṛtūnāmevaitadrūpaṃ kriyate tadṛtuṣvevaitadretaḥ siktam pratiṣṭhāpayati prathamo yajamāno bhakṣayati prathamo retaḥ parigṛhṇānītyatho apyuttamo mayyuttame retaḥ pratitiṣṭhādityupahūta upahvayasveti somamevaitatkurvanti

Five partake of that (whey remaining in the spoon),--viz. the Hotri, the Adhvaryu, the Brahman, the Âgnîdhra, and the Sacrificer; for five are the seasons, so that the characteristic nature of the seasons is thereby obtained; and the seed that is cast is firmly implanted in the seasons. The sacrificer partakes of it first, thinking, 'May I first obtain seed!' But also last (he partakes of it), thinking, 'May seed remain in me last of all!' By saying, 'Invited,--invite thou!' they make it (the whey to resemble) the Soma.