The works of Ādi Śaṅkarācārya

Chāndogyopaniṣadbhāṣyam

Verse 300

तेजसः सोम्याश्यमानस्य योऽणिमास ऊर्ध्वः समुदीषति सा वाग्भवति ॥ ४ ॥

In plain words

Of fiery nourishment being consumed, O gentle one, whatever subtle essence rises upward becomes speech.

Close to the Sanskrit

Of fire being eaten, O gentle one, whichever subtle essence rises upward, that becomes speech.