Matsya Purana — The Viśokā-Saptamī Vow
माघे कृष्णतिलैः स्नात्वा षष्ठ्यां वै शुक्लपक्षतः कृताहारः कृसरया दन्तधावनपूर्वकम् उपवासव्रतं कृत्वा ब्रह्मचारी भवेन्निशि //
māghe kṛṣṇatilaiḥ snātvā ṣaṣṭhyāṃ vai śuklapakṣataḥ kṛtāhāraḥ kṛsarayā dantadhāvanapūrvakam upavāsavrataṃ kṛtvā brahmacārī bhavenniśi //
In the month of Māgha, having bathed with water mixed with black sesame (kṛṣṇa-tila), on the sixth lunar day of the bright fortnight one should first cleanse the teeth and then eat only kṛsarā (a simple rice-and-pulse dish). Thereafter, having undertaken the vow of fasting (upavāsa-vrata), one should observe brahmacarya (celibate restraint) at night.
This verse is not about pralaya; it prescribes a Māgha-month religious observance (bathing, regulated food, fasting, and night-time brahmacarya) as a means of purification and merit.
It frames dharma as disciplined self-restraint: even householders (and rulers) are encouraged to adopt periodic fasting, purity practices, and sexual restraint on vrata days to cultivate self-control and religious merit.
The significance is ritual (not architectural): Māgha snāna with black sesame, eating only kṛsarā after tooth-cleaning, undertaking upavāsa, and observing brahmacarya at night are given as the procedural steps of the vow.