Maitri (Maitrāyaṇīya) Upaniṣad 2.6

2.6

prajāpatirvā eṣo'gre'tiṣṭhatsa nāramataikaḥ sa ātmanamabhidhyāyadbavhīḥ prajā asṛjatta asyaivātmaprabuddhā aprāṇā sthāṇuriva tiṣṭhamānā apaśyatsa nāramata so'manyataitāsaṃ pratibodhanāyābhyantaraṃ prāviśānītyatha sa vāyumivātmānaṃ kṛtvābhyantaraṃ prāviśatsa eko nāviśatsa pañcadhātmānaṃ pravibhajyocyate yaḥ prāṇo'pānaḥ samāna udāno vyāna iti ||

6. “Verily, in the beginning Prajāpati stood alone. He had

no enjoyment, being alone. He then, by meditating upon himself (_ātmānam_), created numerous offspring.

[a] He saw them inanimate and lifeless, like a stone, standing like a post. He had no enjoyment. He then thought to himself: 'Let me enter within, in order to animate them.'

[b] He made himself like wind and sought to enter within. As one, he was unable. So he divided himself fivefold—he who is spoken of as the Prāṇa breath, the Apāna breath, the Samāna breath, the Udāna breath, the Vyāna breath.