Mbh 12.349.2a

"Vaisampayana said, 'When the diverse divisions of the Pandava and the Kuru armies were drawn up in the array for the battle and when Arjuna became cheerless, the holy one himself explained the question of what is the end and what is not the end attained by persons of different characters. I have before this recited to thee the words of the holy one. The religion preached by the holy one on that occasion is difficult of comprehension. Men of uncleansed souls cannot apprehend it at all. Having created this religion in days of yore, viz., in the Krita age, in perfect consonance with the Samans, it is borne, O king, by the Supreme Lord, viz., Narayana, himself. This very topic was raised by the highly blessed Partha to Narada (for the latter's discourse) in the midst of the Rishis and in the presence of Krishna and Bhishma. My preceptor, viz., the Island-born Krishna heard what Narada said. Receiving it from the celestial Rishis, O best of kings, my preceptor imparted it to me in exactly the same way in which he had obtained it from the celestial Rishi. I shall now recite it to thee, O monarch, in the same way as it has been received from Narada. Listen, therefore, to me. In that Kalpa when Brahma the Creator, O king, took his birth in the mind of Narayana and issued from the latter's mouth, Narayana himself performed, O Bharata, his Daiva and Paitra rites in accordance with this religion. Those Rishis that subsist upon the froth of water then obtained it from Narayana. From the froth-eating Rishis, this religion was obtained by those Rishis that go by the name of Vaikanasas. From the Vaikanasas, Shoma got it. Afterwards, it disappeared from the universe. After the second birth of Brahma, viz., when he sprang from the eyes of Narayana, O king, the Grandsire (that is, Brahma) then received this religion from Shoma. Having received it thus, Brahma imparted this religion, which has Narayana for its soul, unto Rudra.