Matsya Purana — The Kalyāṇa-Saptamī
यदा तु शुक्लसप्तम्याम् आदित्यस्य दिनं भवेत् सा तु कल्याणिनी नाम विजया च निगद्यते //
yadā tu śuklasaptamyām ādityasya dinaṃ bhavet sā tu kalyāṇinī nāma vijayā ca nigadyate //
But when the bright fortnight’s seventh lunar day (Śukla-saptamī) coincides with Sunday—the day of Āditya (the Sun)—that tithi is called “Kalyāṇinī,” and it is also spoken of as “Vijayā” (the victory-giving day).
This verse does not address Pralaya; it defines an auspicious calendrical conjunction—Śukla-saptamī falling on Sunday—named Kalyāṇinī/Vijayā.
It guides dhārmic timekeeping: kings and householders choose such ‘victory/auspicious’ days for vows, donations, worship, or initiating undertakings, aligning actions with recognized sacred timings.
The ritual significance is calendrical: Sunday + Śukla-saptamī is treated as a specially named auspicious day (Kalyāṇinī/Vijayā), useful for scheduling Surya-related worship and other rites; no specific Vāstu/temple-building rule is stated in this verse.