Matsya Purana — Soma
पूर्णमासव्यतीपातौ यदा पश्येत्परस्परम् तौ तु वै प्रतिपद्यावत् तस्मिन्काले व्यवस्थितौ //
pūrṇamāsavyatīpātau yadā paśyetparasparam tau tu vai pratipadyāvat tasminkāle vyavasthitau //
When the Full-Moon day (Paurṇamāsī) and the Vyatīpāta conjunction are seen to coincide with one another, one should observe both rites in the prescribed order; for at that time those two observances stand conjointly in operation.
This verse is not about pralaya; it is a dharma-ritual instruction focusing on calendrical timing—specifically the combined occurrence of Pūrṇimā and Vyatīpāta.
It guides householders (and rulers responsible for public rites) to follow prescribed observances when powerful calendrical combinations occur, reinforcing disciplined performance of dharma according to time (kāla).
The significance is ritual-timing: when Vyatīpāta coincides with Pūrṇimā, the observance is treated as a conjointly operative occasion, implying heightened attention to proper vrata/pujā procedure on that day.