Śatapatha Brāhmaṇa ("of a hundred paths") 6.4.1.7

6.4.1.7

athaina puṣkaraparṇe sambharati | yonirvai puṣkaraparṇaṃ yonau tadretaḥ siñcati yadvai yonau retaḥ sicyate tatprajaniṣṇu bhavati tanmantreṇopastṛṇāti vāgvai mantro vākpuṣkaraparṇam

And he deposits it on a lotus-leaf (placed on the skin); for the lotus-leaf is the womb, and into the womb he pours that seed; and the seed which is poured into the womb, becomes generative. He spreads that (leaf) with a formula; for the formula is speech, and the lotus-leaf is speech.