Matsya Purana — Pṛthu
ममन्थुर् ब्राह्मणास्तस्य बलाद्देहमकल्मषाः तत्कायान्मथ्यमानात्तु निपेतुर्म्लेच्छजातयः //
mamanthur brāhmaṇāstasya balāddehamakalmaṣāḥ tatkāyānmathyamānāttu nipeturmlecchajātayaḥ //
Then those stainless Brahmins, by the force of their rite, churned his body; and as that body was being churned, the tribes called Mlecchas fell forth (came into being) from it.
This verse is not about Pralaya directly; it presents a creation-style (sarga) motif where new groups arise through a ritual act—“churning” a body—indicating mythic origins rather than cosmic dissolution.
Indirectly, it frames social diversity as arising within a sacred cosmology; for kings and householders, the implied ethic is governance and conduct that recognizes varied communities while upholding dharma guided by Brahminical ritual authority.
The ritual significance is the idea of mantra-tapas “force” (balāt) empowering Brahmins to effect transformation; there is no explicit Vastu or temple-architecture rule in this verse.