Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.1.8

3.9.1.8

atha saumyam | annaṃ vai somo 'nnenaiva tatprajāpatiḥ punarātmānamāpyāyayatānnamenamupasamāvartatānnamanukamātmano 'kurutānneno evaiṣa etadāpyāyate 'nnamenamupasamāvartate 'nnamanukamātmanaḥ kurute

And as to why it comes after that for Sarasvatî,--Sarasvatî is speech, and Soma is food: he who is incomplete by (having only) speech, now becomes indeed an eater of food.