Jaiminīya Upaniṣad Brāhmaṇa 2.5.10

2.5.10

sa u eva daśaputra iti
sapta śīrṣaṇyāḥ prāṇā dvāv avāñcau nābhyāṃ daśamaḥ /

'He is indeed having ten sons';
for the breaths in the head are seven, two are downward, and the tenth is at the navel.