Matsya Purana — Sādhāraṇa Śrāddha: General Ancestral Rite
वैशाखस्य तृतीयायां नवमी कार्त्तिकस्य च पञ्चदशी च माघस्य नभस्ये च त्रयोदशी //
vaiśākhasya tṛtīyāyāṃ navamī kārttikasya ca pañcadaśī ca māghasya nabhasye ca trayodaśī //
The third lunar day (tṛtīyā) of Vaiśākha, the ninth (navamī) of Kārttika, the fifteenth (pañcadaśī) of Māgha, and the thirteenth (trayodaśī) of Nabhasya (Bhādrapada) are declared to be especially auspicious days of observance.
This verse is not about pralaya; it focuses on dharmic timekeeping—identifying particularly auspicious lunar dates for religious observance.
It guides householders (and rulers setting public religious calendars) to prioritize specific tithis for vrata, worship, charity, and merit-making acts—central to maintaining dharma in society.
Ritually, it is a tithi-list used to select high-merit days for pūjā, dāna, japa, and temple services; it does not give direct Vāstu or temple-construction measurements but supports temple ritual scheduling.