Upaniṣads · Chāndogya 7.19

Chāndogya 7.19.1

यदा वै श्रद्दधात्यथ मनुते नाश्रद्दधन्मनुते श्रद्दधदेव मनुते श्रद्धा त्वेव विजिज्ञासितव्येति श्रद्धां भगवो विजिज्ञास इति ॥ ७.१९.१ ॥

When one has faith, then one thinks. One does not think without faith; only with faith does one think. But faith itself must be inquired into. "Venerable sir, I wish to inquire into faith."