Matsyapurana 15.28

15.28

narmadā nāma teṣāṃ tu kanyā toyavahā sarit
bhūtāni yā pāvayati dakṣiṇāpathagāminī //

Something has been said about the three groups of pitṛis who are worshipped by men and have forms, now follows the description of the fourth set of Pitṛis.—25. There is a mânasa region in the upper Brahmâṇḍa which is the abode of Sômapa Pitṛis. They are eternal, the very incarnation of Dharma, and are as venerable as Brahmâ. They are born of Swadhâ, and having attained Brahmahood, by their power of yoga, they carried on the work of past creations and now rest in Mânasa regions. Narmadâ, which flows in the southern part, is the mânasa daughter of the Sômapa Pitṛis that purifies the people by her sacred waters.—26-28.