Matsya Purana — The Ravi-Śayana
भक्ताय दान्ताय च गुह्यमेतद् आख्येयम् आनन्दकरं शिवस्य इदं महापातकभिन् नराणाम् अप्यक्षरं वेदविदो वदन्ति //
bhaktāya dāntāya ca guhyametad ākhyeyam ānandakaraṃ śivasya idaṃ mahāpātakabhin narāṇām apyakṣaraṃ vedavido vadanti //
This secret teaching—joy-giving and belonging to Śiva—should be proclaimed only to one who is devoted and self-controlled. For human beings it shatters even the gravest sins; the knowers of the Veda declare it to be imperishable.
This verse is not about pralaya events; it emphasizes dharmic transmission—confidential Śiva-related knowledge that is said to be imperishable and powerfully purifying.
It sets an ethical rule of instruction: sacred, potent teachings should be entrusted only to qualified persons—devoted and disciplined—implying that rulers/householders must cultivate self-control and also share spiritual knowledge responsibly.
No direct Vāstu or temple-building rule appears here; the ritual takeaway is about adhikāra (eligibility) and the purificatory efficacy of Śiva-centered sacred instruction.