Vishnupurana 3.4.13

3.4.13

tataḥ sa ṛca uddhṛtya ṛgvedaṃ kṛtavān muniḥ
yajūṃṣi ca yajurvedaṃ sāmavedaṃ ca sāmabhiḥ //

There was but one Yajur-veda; but dividing this into four parts, Vyása instituted the sacrificial rite that is administered by four kinds of priests: in which it was the duty of the Adhwaryu to recite the prayers (Yajush) (or direct the ceremony); of the Hotri, to repeat the hymns (Richas); of the Udgátri, to chaunt other hymns (Sáma); and of the Brahman, to pronounce the formulæ called Atharva. Then the Muni, having collected together the hymns called Richas, compiled the Rigveda; with the prayers and directions termed Yajushas he formed the Yajur-veda; with those called Sáma, Sáma-veda; and with the Atharvas he composed the rules of all the ceremonies suited to kings, and the function of the Brahman agreeably to practice.