Jaiminīya Upaniṣad Brāhmaṇa 1.53

In the beginning, this [universe] was indeed twofold: the real and the unreal.

Of the two, that which is the real is the sāman, it is the mind, it is the out-breath; and that which is the unreal is the ṛc, it is speech, it is the in-breath.

Then that which is mind and out-breath, that is the same; and that which is speech and in-breath, that is the same. Mind and out-breath are this abode, and speech and in-breath are this abode. Therefore a man lies down to the right of a woman.

This ṛc desired union with this sāman. He asked her: 'Who are you?' She said: 'I am Sā (she).' 'Then I am indeed Ama (he).'

Because it was Sā and Ama, therefore it became sāman: that is the sāman-nature of the sāman.

'Let us two unite!' 'No,' he said, 'you are my sister. Seek a mate elsewhere!'

She said: 'I find no one with whom I might unite. Let me unite with you alone.' 'Purify yourself then,' he said, 'for you are unpurified.'

She purified herself through that which the inspired poets speak here. She said: 'Where will this [impurified matter] go?' 'Push it away,' he said; 'this is inspired thought; this will become the livelihood of creatures.' 'So be it.' She pushed it away. Therefore this is inspired thought, this is indeed the livelihood of creatures.

He said: 'Purify yourself!' She purified herself with the gāthā; she purified herself with the kumbyā; she purified herself with the nārāśaṃsī; she purified herself with the purāṇa and itihāsa; she purified herself with that taking which they do not sing here.

She said: 'Where will this [impurified matter] go?' 'Push it away,' he said; 'this is inspired thought; this will become the livelihood of creatures.' 'So be it.' She pushed it away. Therefore this is indeed inspired thought, this is indeed the livelihood of creatures.

'Purify yourself further!' he said. / The first khaṇḍa in the seventeenth anuvāka.