The works of Ādi Śaṅkarācārya

Chāndogyopaniṣadbhāṣyam

Verse 20

समान उ एवाय चासौ चोष्णोऽयमुष्णोऽसौ स्वर इतीममाचक्षते स्वर इतिप्रत्यास्वर इत्यमुं तस्माद्वा एतमिमममुंचोद्गीथमुपासीत ॥ २ ॥

In plain words

This breath and that sun are identical; both are warm. They call this breath 'svara' and that sun 'pratyasvara'. Therefore, let a seeker meditate upon this breath and that sun alike as the Udgītha.

Close to the Sanskrit

Equal indeed is this one and that one; warm is this, warm is that. Svara they call this, pratyasvara that. Therefore one should meditate upon this very prana and that sun as the Udgitha.