Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.2.7

6.2.2.7

yadvevaitaṃ vāyave niyutvate | śuklaṃ tūparamālabhate prajāpatiṃ vistrastaṃ yatra devāḥ samaskurvantsa yo 'smātprāṇo madhyata udakrāmattamasminnetena paśunādadhustathaivāsminnayametaddadhāti vāyave bhavati prāṇo vai vāyurniyutvate bhavatyudāno vai niyutaḥ prāṇodānāvevāsminnetaddadhāti śuklo bhavati śuklo hi vāyustūparo bhavati tūparo hi vāyuḥ

And, again, why he slaughters that white, hornless (he-goat);--when the gods restored the relaxed Pragâpati, they, by means of this victim, put into him that out-breathing which had gone out of him; and in like mariner this one now puts it into him. It belongs to Vâyu, because Vâyu is the out-breathing; and to Niyutvat, because the teams are the in-breathing: he thus puts the out-breathing and in-breathing into him. It is white, because Vâyu (the wind) is white; and it is hornless, because Vâyu is hornless.