Matsya Purana — Manvantaras
श्रुत्वा ऋषं परत्वेन श्रुतास्तस्माच्छ्रुतर्षयः अव्यक्तात्मा महात्मा वा-हंकारात्मा तथैव च //
śrutvā ṛṣaṃ paratvena śrutāstasmācchrutarṣayaḥ avyaktātmā mahātmā vā-haṃkārātmā tathaiva ca //
Having heard the seer spoken of as the Supreme, those sages—thus renowned for what they had heard—taught that the Self (Ātman) is of three kinds: the Unmanifest Self (avyakta-ātman), the Great Self (mahātman), and likewise the Ego-Self (ahaṃkāra-ātman).
It frames creation in Sāṅkhya terms: from the Unmanifest (avyakta) arises the Great Principle (mahat), and from that the Ego-principle (ahaṃkāra)—a standard chain used to explain cosmic manifestation and its re-absorption in pralaya.
Indirectly, it grounds dharma in self-knowledge: by discerning the unmanifest, cosmic intellect, and ego, a king or householder can restrain ego-driven action and govern/act with steadiness and detachment—an ethical outcome frequently emphasized in Purāṇic instruction.
No direct Vāstu or ritual rule is stated; the verse supplies metaphysical vocabulary (avyakta–mahat–ahaṃkāra) that later supports Purāṇic temple/ritual symbolism where cosmic principles are mapped onto iconography and sacred space.