The Mukhya Upaniṣads

Aitareya · Adhyāya 1 · Khaṇḍa 3 · The Search for Food, and the Discovery of Who Asks

Passage 6

तच्छ्रोत्रेणाजिघृक्षत्तन्नाशक्नोच्छ्रोत्रेण ग्रहीतुं स यद्धैनच्छ्रोत्रेणाग्रहैष्यच्छ्रुत्वा हैवान्नमत्रप्स्यत् ॥ ६ ॥

In plain words

He tried to seize it with the ear; he was unable to grasp it with the ear. Had he grasped it with the ear, i.e. merely by hearing it, then merely by with the ear, i.e. merely by hearing it, one would have been satisfied by food.