The works of Ādi Śaṅkarācārya

Svātmaprakāśikā

Verse 71

एवं तत्त्वविचाराब्धौ निमग्नानां सदा नृणाम् ।परमाद्वेतविज्ञानमपरोक्षं न संशयः ॥ ६८ ॥

In plain words

So it is: for people who stay plunged in the ocean of inquiry into what is real, the supreme knowledge of non-duality becomes aparokṣa — immediate, firsthand, not something heard about. There is no doubt in this.

Close to the Sanskrit

Thus, for people always immersed in the ocean of inquiry into reality, the supreme non-dual knowledge is immediate — there is no doubt.