Aitareya Upaniṣad 1.2.4

1.2.4

agnir vāg bhūtvā mukhaṃ prāviśat.
vāyuḥ prāṇo bhūtvā nāsike prāviśat.
ādityaś cakṣur bhūtvākṣiṇī prāviśat.
diśaḥ śrotraṃ bhūtvā karṇau prāviśan.
oṣadhivanaspatayo lomāni bhūtvā tvacaṃ prāviśan.
candramā mano bhūtvā hṛdayaṃ prāviśat.
mṛtyur apāno bhūtvā nābhiṃ prāviśat.
āpo reto bhūtvā śiśnaṃ prāviśan.

4. Fire became speech, and entered the mouth. Wind became breath, and entered the nostrils. The sun became sight, and entered the eyes. The quarters of heaven became hearing, and entered the ears. Plants and trees became hairs, and entered the skin. The moon became mind, and entered the heart. Death became the out-breath (_apāna_), and entered the navel. Waters became semen, and entered the virile member.