Matsya Purana — Measures of Time: Caturyuga Computation
त्रेतादौ संहता वेदाः केवलं धर्मसेतवः संरोधादायुषश्चैव व्यस्यन्ते द्वापरे च ते ऋषयस्तपसा वेदान् अहोरात्रमधीयते //
tretādau saṃhatā vedāḥ kevalaṃ dharmasetavaḥ saṃrodhādāyuṣaścaiva vyasyante dvāpare ca te ṛṣayastapasā vedān ahorātramadhīyate //
In the beginning of the Tretā age, the Vedas remain compact and undivided, serving solely as bridges that uphold dharma. But owing to constraint and the shortening of lifespan, they are arranged into divisions in the Dvāpara age. Then the seers, through ascetic discipline (tapas), study the Vedas day and night.
It does not describe cosmic pralaya directly; instead, it explains a yuga-based decline—shortened lifespan and increasing limitation—which leads to the Vedas being organized into divisions in Dvāpara for preservation and accessibility.
It frames dharma as sustained by scripture: as human capacity diminishes with time, rulers and householders must rely on organized śāstra and learned ṛṣis/teachers to maintain dharma—supporting education, recitation, and right practice rather than assuming earlier-yuga capacities.
No Vāstu or temple-rule detail is stated; the ritual takeaway is that Vedic study (svādhyāya) and disciplined practice (tapas) are presented as the means by which the Vedas—and thus ritual correctness—are maintained in later yugas.