Prashna Upanishad 6.7

तान् होवाचैतावदेवाहमेतत् परं ब्रह्म वेद । नातः
परमस्तीति ॥ ६.७॥

tān hovācaitāvadevāhametat paraṃ brahma veda . nātaḥ
paramastīti .. 6.7..

Pippalada said to them: Thus far, indeed, I know the Supreme Brahman; there is nothing higher than this.