Shatapatha Brahmana 14.3.1.35

14.3.1.35

atha yaiṣā patnyai vratadughā tāmudgātṛbhyo dadāti patnīkarmeva vā ete'tra kurvanti yadudgātārastasmāttāmudgātṛbhyo dadāti

And that cow which yielded the fast-milk for the (Sacrificer's) wife he gives to the chanters, for it is they, the Udgâtris, that do, as it were, the wife's work on this occasion: therefore he gives it to the chanters.