Kauṣītaki Upaniṣad 2.13

2.13

This Brahman shines forth indeed when one speaks with speech, and it dies when one does not speak. His splendour goes to the eye alone, the life (prâna) to breath (prâna).
This Brahman shines forth indeed when one sees with the eye, and it dies when one does not see. Its splendour goes to the ear alone, the life (prâna) to breath (prâna).
This Brahman shines forth indeed when one hears with the ear, and it dies when one does not hear. Its splendour goes to the mind alone, the life (prâna) to breath (prâna).
This Brahman shines forth indeed when one thinks with the mind, and it dies when one does not think. Its splendour goes to the breath (prâna) alone, and the life (prâna) to breath (prâna).
Thus all these deities (the senses, &c.), having entered breath or life (prâna) alone, though dead, do not vanish; and out of very breath (prâna) they rise again. And if two mountains, the southern and northern, were to move forward trying to crush him who knows this, they would not crush him. But those who hate him and those whom he hates, they die around him.