Shatapatha Brahmana 1.1.1.10

1.1.1.10

sa vā āraṇyamevāśnīyāt | yā vāraṇyā oṣadhayo yadvā vṛkṣyaṃ tadu ha smāhāpi barkurvārṣṇo māsānme pacata na vā etesāṃ havirgṛhṇantīti tadu tathā na kuryādvrīhiyavayorvā etadupajaṃ yacamīdhānyaṃ tadvrīhiyavāvevaitena bhūyāṃsau karoti tasmādāraṇyamevāśnīyāt

Let him therefore eat only what grows in the forest, be it forest plants or the fruit of trees. And in regard to this point Barku Vârshna said: 'Cook ye beans for me, for no offering is made of them!' This, however, he should not do; for pulse serves as an addition to rice and barley; and hence he increases the rice and barley by means of it: let him therefore eat only what grows in the forest.