Matsya Purana — Soma
सिनीवालीप्रमाणं तु क्षीणशेषो निशाकरः अमावास्या विशत्यर्कं सिनीवाली तदा स्मृता //
sinīvālīpramāṇaṃ tu kṣīṇaśeṣo niśākaraḥ amāvāsyā viśatyarkaṃ sinīvālī tadā smṛtā //
When the Moon remains only as a waning remnant—measured by the Sinīvālī measure—and on the new-moon day it approaches, entering into conjunction with, the Sun, that time is remembered as Sinīvālī.
This verse does not discuss Pralaya; it gives a technical calendrical definition connected to the Moon’s waning phase and its conjunction with the Sun at Amāvāsyā.
It supports dharmic duty indirectly by defining correct time-reckoning: kings and householders rely on accurate tithi markers like Sinīvālī/Amāvāsyā to schedule śrāddha, dāna, vows, and other rites at the proper time.
Ritually, it helps determine precise new-moon timing (Amāvāsyā) and the Sinīvālī phase—useful for selecting auspicious/required moments for observances, offerings, and ancestral rites based on Panchāṅga calculations.