CHĀNDOGYA UPANISHAD · 3.15.5

अथ यदवोचं भूः प्रपद्य इति पृथिवीं प्रपद्येऽन्तरिक्षं
प्रपद्ये दिवं प्रपद्य इत्येव तदवोचम् ॥ ३.१५.५॥

atha yadavocaṃ bhūḥ prapadya iti pṛthivīṃ prapadye’ntarikṣaṃ
prapadye divaṃ prapadya ityeva tadavocam ॥ 3.15.5॥

'When I said, I turn to Bhûh, what I said is, I turn to the earth, the sky, and heaven.'

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)