Upaniṣads · Chāndogya 7.17

Chāndogya 7.17.1

यदा वै विजानात्यथ सत्यं वदति नाविजानन्सत्यं वदति विजानन्नेव सत्यं वदति विज्ञानं त्वेव विजिज्ञासितव्यमिति विज्ञानं भगवो विजिज्ञास इति ॥ ७.१७.१ ॥

When one truly knows, then one speaks the truth. One who does not know does not speak the truth; only one who knows speaks the truth. But knowledge itself must be inquired into. "Venerable sir, I wish to inquire into knowledge."