CHĀNDOGYA UPANISHAD · 3.12.8

अयं वाव स यो ऽयम् अन्तः पुरुष आकाशः ।
यो वै सो ऽन्तः पुरुष आकाशः ॥

ayaṃ vāva sa yo ’yam antaḥ puruṣa ākāśaḥ ।
yo vai so ’ntaḥ puruṣa ākāśaḥ ॥

And the ether which is around us, is the same as the ether which is within us. And the ether which is within us,

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