Matsya Purana — Catalogue of the Eighteen Puranas
श्रुतीनां यत्र कल्पादौ प्रवृत्त्यर्थं जनार्दनः मत्स्यरूपेण मनवे नरसिंहोपवर्णनम् //
śrutīnāṃ yatra kalpādau pravṛttyarthaṃ janārdanaḥ matsyarūpeṇa manave narasiṃhopavarṇanam //
Here it is described how, at the beginning of a kalpa, Janārdana—assuming the form of the Fish (Matsya) to set the Śruti (the Vedas) in motion—expounded to Manu the account of the Narasiṃha manifestation.
It places Matsya’s appearance at the kalpa’s beginning as a restoration/activation of śruti—implying a post-dissolution reset where divine intervention re-establishes Vedic continuity.
By grounding dharma in śruti, it implies that royal and household duties must align with Vedic authority; Manu, the archetypal lawgiver, receives divine instruction as the basis for orderly conduct.
No direct Vāstu or temple-rule detail appears in this verse; its ritual takeaway is the primacy of śruti as the source that authorizes rites and correct practice at the start of a cosmic cycle.