CHĀNDOGYA UPANISHAD · 1.13.4

दुग्धे ऽस्मै वाग् दोहं यो वाचो दोहः ।
अन्नवान् अन्नादो भवति ।
य एताम् एवं साम्नाम् उपनिषदं वेदोपनिषदं वेद ॥

dugdhe ’smai vāg dohaṃ yo vāco dohaḥ ।
annavān annādo bhavati ।
ya etām evaṃ sāmnām upaniṣadaṃ vedopaniṣadaṃ veda ॥

Speech yields the milk, which is the milk of speech itself to him who knows this Upanishad (secret doctrine) of the Sâmans in this wise. He becomes rich in food, and able to eat food,--yea, able to eat food.

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)