Matsya Purana — The Attendant Hosts of the Sun and Moon: Monthly Gaṇas
क्षीयन्ते च ताः शुक्लाः कृष्णा ह्याप्याययन्ति च एवं दिनक्रमात्पीते देवैश्चापि निशाकरे //
kṣīyante ca tāḥ śuklāḥ kṛṣṇā hyāpyāyayanti ca evaṃ dinakramātpīte devaiścāpi niśākare //
Those lunar portions (kalās) diminish in the bright fortnight (śukla), and in the dark fortnight (kṛṣṇa) they are indeed replenished. Thus, as the days proceed, the Night-maker (the Moon) is, as it were, drunk by the gods.
It does not describe Pralaya directly; it explains the regulated cosmic process of lunar waxing and waning as part of the ongoing maintenance of time and order.
By grounding ritual and calendrical observances in the lunar fortnight system, it supports dharmic scheduling—fasts, offerings, and royal/household rites aligned to Śukla- and Kṛṣṇa-pakṣa.
Ritually, it points to Soma/Moon-based calendrics used for selecting tithis and pakṣas for yajñas, vratas, and temple worship timings (rather than giving a direct Vāstu rule).