त्रीण्यात्मनेऽकुरुतेति मनो वाचं प्राणं तान्यात्मनेऽकुरुत ।अन्यत्रमना अभूवं नादर्शमन्यत्रमना अभूवं नाश्रौषमिति मनसा ह्येव पश्यति मनसा शृणोति ।कामः संकल्पो विचिकित्सा श्रद्धाश्रद्धा धृतिरधृतिर्ह्रीर्धीर्भीरित्येतत्सर्वं मन एव ।तस्मादपि पृष्ठत उपस्पृष्टो मनसा विजानाति ।यः कश्च शब्दो वागेव सा ।एषा ह्यन्तं आयत्तैषा हि न ।प्राणोऽपानो व्यान उदानः समानोऽन इत्येतत्सर्वं प्राण एव ।एतन्मयो वा अयमात्मा ।वाङ्मयो मनोमयः प्राणमयः ॥बृह. १,५.३ ॥
In plain words
"Three he made for himself" — mind, speech and breath; these he made for himself. Men say, "My mind was elsewhere, I did not see; my mind was elsewhere, I did not hear" — for it is with the mind that one sees and with the mind that one hears. Desire, resolve, doubt, faith and unfaith, steadfastness and unsteadfastness, shame, understanding and fear — all this is mind alone. Therefore even when one is touched from behind one knows it with the mind. Whatever sound there is, that is speech; for speech is directed to an end, and it is not itself the end. The out-breath, the down-breath, the diffused breath, the up-breath and the even breath — all this is the breath alone. This self is made of these: it is made of speech, made of mind, made of breath.