Śatapatha Brāhmaṇa ("of a hundred paths") 7.3.1.37

7.3.1.37

tadāhuḥ | yadārdraṃ retaḥ śuṣkāḥ sikatā nivapati kathamasyaitā ārdrā retorūpam bhavantīti raso vai candāṃsyārdra u vai rasastadyadenāścandobhirnivapatyevamu hāsyaitā ārdrā retorūpam bhavanti

As to this they say, 'As seed is moist, and he scatters dry sand, how does it become moist for him, after the manner of seed?' Well, the metres are vital sap, and vital sap is moist; and inasmuch as he scatters that (sand) with metres, it is thus that it becomes moist for him, after the manner of seed.