Śatapatha Brāhmaṇa ("of a hundred paths") 13.3.8.1

13.3.8.1

athātaḥ prāyaścittīnām yadyaśvo vaḍavāṃ skandedvāyavyam payo'nunirvapedvāyurvai retasāṃ vikartā prāṇo vai vāyuḥ prāṇo hi retasāṃ vikartā retasaivāsmiṃstadreto dadhāti

Now, then, of the expiations. If the sacrificial horse were to couple with a mare, let him in addition prepare a milk (oblation) to Vâyu;--Vâyu doubtless is the transformer of seeds, for Vâyu (the wind) is the vital air, and the vital air is the transformer of seeds: by means of seed he thus puts seed into it.