मध्यप्राणं सुषुप्तौ स्वजनिमनुविशन्त्यग्निसूर्यादयोऽमीवागाद्याः प्राणवायुं तदिह निगदिता ग्लानिरेषां न वायोः ।तेभ्यो दृश्यावभासो भ्रम इति विदितः शुक्तिकारौप्यकल्पःप्राणायामव्रतं तच्छ्रुतिशिरसि मतं स्वात्मलब्धौ न चान्यत् ॥ ३९ ॥
In plain words
In deep sleep fire, the sun and the other deities return to their source in the central Prāṇa. Speech and the senses merge into that vital current; the fatigue belongs to them, never to Prāṇa itself. Their display of objects is an error like silver seen in a shell. The Upaniṣads, the crown of Śruti, teach Prāṇāyāma—the discipline of breath—solely for attaining one's own Ātma, the Self.
Close to the Sanskrit
In deep sleep fire, the sun and the other deities enter the central Prāṇa, each returning to its source. Speech and the other organs enter Prāṇa; their weariness is spoken of here, not Prāṇa's. The appearance of objects from them is known as error, like silver in mother-of-pearl. At the crown of Śruti, the discipline of Prāṇāyāma is held to be solely for attaining one's own Ātma, and for nothing else.