Jaiminīya Upaniṣad Brāhmaṇa 3.35.2

3.35.2

pataṅgam aktam iti
prāṇo vai pataṅgaḥ
patann iva hy eṣv aṅgeṣv ati ratham udīkṣate
pataṅga ity ācakṣate /

"The bird anointed": breath is indeed the bird. For flying, as it were, through these limbs, it gazes beyond the chariot; therefore they call it the bird.