Matsya Purana — Bhīma-Dvādaśī
एकादश्यां निराहारः समभ्यर्च्य च केशवम् रात्रिं च सकलां स्थित्वा स्नानं च पयसा तथा //
ekādaśyāṃ nirāhāraḥ samabhyarcya ca keśavam rātriṃ ca sakalāṃ sthitvā snānaṃ ca payasā tathā //
On the Ekādaśī day, one should fast completely, duly worship Keśava (Viṣṇu), keep vigil through the entire night, and then perform bathing with milk as well.
This verse is not about Pralaya; it focuses on vrata-dharma—Ekādaśī fasting and Keśava worship as a purificatory discipline.
It prescribes a householder-friendly devotional discipline: fasting (nirāhāra), worship of Viṣṇu, night-long vigil (jāgaraṇa), and ritual bathing—acts considered dharmic self-restraint and merit-producing conduct.
The ritual significance is explicit: Ekādaśī upavāsa, Keśava-pūjā, all-night vigil, and a milk-bath (payasā snāna), indicating a heightened purity rite within Vaiṣṇava observance.