Matsya Purana — The Aśūnyaśayana Vrata
*श्रीभगवानुवाच श्रावणस्य द्वितीयायां कृष्णायां मधुसूदनः क्षीरार्णवे सपत्नीकः सदा वसति केशवः //
*śrībhagavānuvāca śrāvaṇasya dvitīyāyāṃ kṛṣṇāyāṃ madhusūdanaḥ kṣīrārṇave sapatnīkaḥ sadā vasati keśavaḥ //
The Blessed Lord said: On the second lunar day (Dvitiya) of the dark fortnight in the month of Śrāvaṇa, Madhusūdana—Keśava—ever dwells in the Ocean of Milk, together with His consort.
It does not describe Pralaya directly; it situates Viṣṇu (Keśava) in His cosmic abode, the Ocean of Milk, emphasizing His perpetual, sustaining presence behind cosmic order.
By mapping a specific tithi (Śrāvaṇa Kṛṣṇa Dvitīyā) to Keśava’s divine presence, it supports householders and rulers in structuring dharmic life around observances—timely worship, vows, and disciplined calendrical practice.
Ritually, it highlights a tithi suited for Keśava-oriented worship/vrata; architecturally it implies no direct Vāstu rule, but supports temple ritual scheduling (nitya/naimittika pūjā) aligned to the lunar calendar.