Jaiminīya Upaniṣad Brāhmaṇa 2.6.9

2.6.9

sa yadi brūyād daśa ma āgāyeti prāṇa udgītha ity eva vidvān daśa manasā dhyāyet
sapta śīrṣaṇyāḥ prāṇā dvāv avāñcau nābhyāṃ daśamaḥ
daśa haivāsyājāyante /

If he should say: “Chant for me for ten”, knowing that breath is the udgītha, he should mentally focus on ten.
Seven are the breaths in the head, two downward, the tenth is at the navel.
Ten indeed are born to him.