Matsya Purana — Yuga Durations
तदा सत्यं च शौचं च धर्मश्चैव विवर्धते सद्भिराचरितं कर्म क्रियते ख्यायते च वै //
tadā satyaṃ ca śaucaṃ ca dharmaścaiva vivardhate sadbhirācaritaṃ karma kriyate khyāyate ca vai //
Then truthfulness and purity increase, and dharma flourishes as well; the deeds practiced by the virtuous are performed (by others) and indeed become widely renowned.
This verse does not describe pralaya directly; it teaches moral causality—when the virtuous model truth and purity, dharma increases and becomes established in society.
It frames leadership and domestic life as exemplary: a king or householder should embody satya (truth) and śauca (purity), because public conduct imitates the ‘good,’ making dharma both practiced and socially celebrated.
No specific vāstu or temple rule appears here; the ritual takeaway is that śauca (purity) is a foundational prerequisite for dharmic action and for rites to be considered properly performed.