Chāndogya Upaniṣad 8.7.4

8.7.4

tau ha prajāpatir uvāca ya eṣo 'kṣiṇi puruṣo dṛṣyata eṣa ātmeti hovāca \
etad amṛtam abhayam etad brahmeti \
atha yo ayaṃ bhagavo 'psu parikhyāyate yaś cāyam ādarśe katama eṣa iti \
eṣa u evaiṣu sarveṣvannteṣu parikhyāyata iti hovāca \\807.4\

4. Then Prajāpati said to the two: 'That Person who is seen in the eye—He is the Self (Ātman) of whom I spoke. That is the immortal, the fearless. That is Brahma.'

'But this one, Sir, who is observed in water and in a mirror—which one is he?'

'The same one, indeed, is observed in all these,' said he.