Matsya Purana — Characteristics of Dvāpara and Kali Yugas
गुणहीनास्तु तिष्ठन्ति धर्मस्य द्वापरस्य तु तथैव संध्या पादेन अंशस्तस्यां प्रतिष्ठितः //
guṇahīnāstu tiṣṭhanti dharmasya dvāparasya tu tathaiva saṃdhyā pādena aṃśastasyāṃ pratiṣṭhitaḥ //
In the Dvāpara age, people remain lacking in virtues; and likewise, the transitional period (sandhyā) is established with only a quarter share of that dharma.
It does not describe pralaya directly; it explains cyclical time by stating that dharma diminishes across yugas, especially in transitional junctions (sandhyā), which is part of the broader cosmic cycle that also includes dissolution and renewal.
By warning that virtue declines in Dvāpara, it implies kings and householders must uphold dharma more consciously—through truthfulness, restraint, charity, and just governance—because social morality no longer supports righteousness as strongly as in earlier ages.
No explicit Vāstu or temple rule is stated; the takeaway is contextual—ritual discipline and dharmic observances become more crucial in later yugas when innate virtue is weaker.