Matsya Purana — The Viśokā-Saptamī Vow
अनेन विधिना सर्वम् उभयोरपि पक्षयोः कृत्वा यावत्पुनर्माघशुक्लपक्षस्य सप्तमी //
anena vidhinā sarvam ubhayorapi pakṣayoḥ kṛtvā yāvatpunarmāghaśuklapakṣasya saptamī //
Having performed everything in this manner in both fortnights—the dark and the bright halves—one should continue again until the Saptamī of the bright fortnight of Māgha.
This verse is not about Pralaya; it is a calendrical instruction for continuing a prescribed observance across both lunar fortnights until Māgha Śukla Saptamī.
It frames dharma as disciplined continuity: a householder (and by extension a ruler setting an example) should follow the prescribed rite through both pakṣas and maintain it until the stated tithi, showing steadiness in vows and ritual obligations.
Ritually, it gives tithi-bound duration: the observance is to be carried out in both the dark and bright halves and continued until Māgha Śukla Saptamī—useful for vrata scheduling and ritual planning.