Matsya Purana — The Observance of Ananta-Tritiya
पञ्चगव्यं च बिल्वं च प्राशयेत्क्रमशस्तदा एतद्भाद्रपदाद्यं तु प्राशनं समुदाहृतम् //
pañcagavyaṃ ca bilvaṃ ca prāśayetkramaśastadā etadbhādrapadādyaṃ tu prāśanaṃ samudāhṛtam //
Then one should ingest, in the proper sequence, pañcagavya and bilva (the bael fruit/leaf). This is declared to be the prescribed prāśana—ritual ingestion—for the commencement of the month of Bhādrapada.
This verse does not discuss pralaya; it focuses on ācamana/śuddhi-type monthly observance—ritual purification through prescribed ingestion at the start of Bhādrapada.
It frames a practical āchāra guideline: a householder (and by extension a king as moral exemplar) maintains ritual purity and seasonal discipline by observing month-beginning rites such as prāśana with pañcagavya and bilva.
The significance is ritual (not architectural): pañcagavya is a classic purificatory substance in Purāṇic practice, and bilva is a sanctifying plant; together they mark a calendrical vrata-style prāśana for Bhādrapada’s commencement.