The works of Ādi Śaṅkarācārya

Bṛhadāraṇyakopaniṣadbhāṣyam

Verse 231

यद्वै तन्न विजानाति विजानन्वै तन्नविजानाति न हि विज्ञातुर्विज्ञातेर्विपरि-लोपो विद्यतेऽविनाशित्वान्न तु तद्द्वितीय-मस्ति ततोऽन्यद्विभक्तं यद्विजानीयात् ॥

In plain words

When he seems not to know anything in that state, he is still the knower—knowing is simply what he is, and it can never stop, because it can never die. There is no second thing out there, apart from him, left for him to know.

Close to the Sanskrit

That which he does not cognize there—cognizing, indeed, he does not cognize there; for there is no loss of the knower's cognition, because it is imperishable. But there is not a second thing, other than that, separate, which he could cognize.