Śatapatha Brāhmaṇa ("of a hundred paths") 8.3.3.7

8.3.3.7

sa vai niruktāni cāniruktāni copadadhāti | sa yatsarvāṇi niruktānyupādhāsyadantavaddhānnamabhaviṣyadakṣeṣyata hātha yatsarvāṇyaniruktāni paro 'kṣaṃ hānnamabhaviṣyanna hainadadrakṣyaṃścana niruktāni cāniruktāni copadadhāti tasmānniruktamannamadyamānaṃ na kṣīyate

He lays down both defined and undefined (metres). Were he to lay down such as are all defined, then the food would have an end, it would fail; and (were he to lay down) such as are all undefined, then the food would be invisible, and one would not see it at all. He lays down both defined and undefined ones: hence the defined (certain) food which is eaten does not fail.