Matsya Purana — The Array of the Gods: Description of the Vaiṣṇava Host and the Lokapālas
स्वस्त्यस्तु देवेभ्य इति बृहस्पतिरभाषत स्वस्त्यस्तु दानवानीक उशना वाक्यमाददे //
svastyastu devebhya iti bṛhaspatirabhāṣata svastyastu dānavānīka uśanā vākyamādade //
“May there be well-being for the gods,” said Bṛhaspati. “May there be well-being for the host of Dānavas,” replied Uśanā, taking up the word in turn.
This verse does not discuss pralaya; it highlights a formal exchange of auspicious benedictions between rival camps, emphasizing order and restraint rather than cosmic dissolution.
It models dhārmic speech: even amid rivalry, one should speak words that preserve social stability and goodwill—an ideal for kings (statecraft and diplomacy) and householders (non-hostile conduct and auspicious speech).
The phrase “svasty astu” is a ritual benediction used in auspicious openings and formal proclamations; while not a Vāstu rule, it aligns with the Purāṇic practice of beginning rites and assemblies with blessings for well-being.