Kauṣītaki Upaniṣad 1.6.8

1.6.8

satyam iti brūyāt /

To him he says: ‘Who am I?’ He should say: ‘The Real.’ ‘What is that, namely the Real (_satyam_)?’ ‘Whatever is other than the sense-organs (_deva_) and the vital breaths (_prāṇa_)—that is the actual (_sat_). But as for the sense-organs and the vital breaths—that is the yon (_tyam_). This is expressed by this word “_satyam_” (‘the Real’). It is as extensive as this world-all. You are this world-all.’