In the beginning, my dear, this universe was the existent
only, one alone, without a second. (Chandogya Upanishad VI, 2, 1)
Where one sees nothing else, hears nothing else, understands
nothing else – that is the Fullness. (Chandogya Upanishad VII, 24, 1)
Atman, indeed, is this all. (Chandogya Upanishad VII, 25, 1)
Verily, this all is Brahman. (Chandogya Upanishad III, 14,
1)
Brahman, indeed, is this all’ Atman verily, was this
universe, one alone, in the beginning. (Aitareya Upanishad I 1, 1)