Chāndogya Upaniṣad 5.2.1

5.2.1

sa hovāca kiṃ me annaṃ bhaviṣyatīti \
yat kiṃcid idam ā śvabhya ā śakunibhya iti hocuḥ \
tad vā etad anasyānnam \
ano ha vai (S ) nāma pratyakṣam \
na ha vā evaṃvidi kiṃcanānannaṃ (S ) \\502.1\

1. It said: ‘What will be my food?’

‘Whatever there is here, even to dogs and birds,’ they said.

So this, verily, is the food (anna) of breath (ana). Verily, breath is its evident name. Verily, in the case of one who knows this, there is nothing whatever that is not food.