Chāndogya Upaniṣad 3.12.7

3.12.7

yad vai tad brahmetīdaṃ vāva tad yo 'yaṃ bahirdhā puruṣād ākāśaḥ \
yo vai sa bahirdhā puruṣād ākāśaḥ \\312.7\

7. Verily, what is called Brahma—that is the same as what the space outside of a person is. Verily, what the space outside of a person is— that is the same as what the space within a person is. Verily, what the space within a person is— that is the same as what the space here within the heart is. That is the Full, the Non-active. Full, non-active prosperity he obtains who knows this.