BṚHADĀRAṆYAKA UPANISHAD · 1.4.9

तद् आहुर् यद् ब्रह्मविद्यया सर्वं भविष्यन्तो मनुष्या मन्यन्ते ।
किम् उ तद् ब्रह्मावेद् यस्मात् तत् सर्वम् अभवद् इति ॥

tad āhur yad brahmavidyayā sarvaṃ bhaviṣyanto manuṣyā manyante ।
kim u tad brahmāved yasmāt tat sarvam abhavad iti ॥

Here they say: 'If men think that by knowledge of Brahman they will become everything, what then did that Brahman know, from whence all this sprang?'

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