BṚHADĀRAṆYAKA UPANISHAD · 4.3.30

यद् वै तन् न विजानाति विजानन् वै तन् न विजानाति ।
न हि विज्ञातुर् विज्ञातेर् विपरिलोपो विद्यते ऽविनाशित्वात् ।
न तु तद् द्वितीयम् अस्ति ततो ऽन्यद् विभक्तं यद् विजानीयात् ॥

yad vai tan na vijānāti vijānan vai tan na vijānāti ।
na hi vijñātur vijñāter viparilopo vidyate ’vināśitvāt ।
na tu tad dvitīyam asti tato ’nyad vibhaktaṃ yad vijānīyāt ॥

'And when (it is said that) there (in the Sushupti) he does not know, yet he is knowing, though he does not know. For knowing is inseparable from the knower, because it cannot perish. But there is then no second, nothing else different from him that he could know.

F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)