Shatapatha Brahmana 1.7.1.14

1.7.1.14

tannidadhāti | vasoḥ pavitramasīti yajño vai vasustasmādāha vasoḥ pavitramasīti śatadhāraṃ sahasradhāramityupastautyevainadetanmahayatyeva yadāha śatadhāraṃ sahasradhāramiti

He puts it down, with the text (Vâg. S. I, 3 a), 'Vasu's means of purification (pavitram) art thou!'--Vasu, indeed, is the sacrifice: for this reason he says, 'Vasu's means of purification art thou! flowing in a hundred streams, flowing in a thousand streams!'--he praises and eulogises it when he says, 'flowing in a hundred streams, flowing in a thousand streams.'