Matsya Purana — Manvantaras
संन्यासः कर्मणां न्यासः कृतानामकृतैः सह कुशलाकुशलाभ्यां तु प्रहाणं न्यास उच्यते //
saṃnyāsaḥ karmaṇāṃ nyāsaḥ kṛtānāmakṛtaiḥ saha kuśalākuśalābhyāṃ tu prahāṇaṃ nyāsa ucyate //
Renunciation (saṃnyāsa) is the laying down of actions—both those already done and those yet to be done; and the abandonment of both the meritorious (kuśala) and the unmeritorious (akuśala) is what is called ‘laying down’ (nyāsa).
This verse does not discuss pralaya directly; it defines saṃnyāsa as inner relinquishment—giving up attachment to actions and to both merit and demerit—aimed at liberation rather than cosmology.
It frames the transition-point where duty-bound action (for a householder or king) is ultimately to be surpassed by renunciation: one must eventually relinquish not only wrongful acts but also attachment to ‘good’ merit, treating both performed and unperformed obligations as laid down when entering saṃnyāsa.
No vastu or temple-building rule is stated here; the ritual takeaway is conceptual—‘nyāsa’ is defined as abandoning the entire field of karmic accounting (puṇya/pāpa), rather than prescribing a specific rite.