Chāndogya Upaniṣad 7.2.3

7.2.3

yad vai vāṅ nābhaviṣyan na dharmo nādharmo vyajñāpayiṣyan na satyaṃ nānṛtaṃ na sādhu nāsādhu na hṛdayajño nāhṛdayajñaḥ \

men, beasts and birds, grass and trees, animals together with worms, flies, and ants, right and wrong, true and false, good and bad, pleasant and unpleasant. Verily, if there were no speech, neither right nor wrong would be known, neither true nor false, neither good nor bad, neither pleasant nor unpleasant. Speech, indeed, makes all this known. Reverence Speech.