Matsya Purana — Narasimha’s Victory over Hiraṇyakaśipu and the Catalogue of Apocalyptic Omens
सहस्रशीर्षा नागो वै हेमतालध्वजः प्रभुः शेषो ऽनन्तो महाभागो दुष्प्रकम्प्यः प्रकम्पितः //
sahasraśīrṣā nāgo vai hematāladhvajaḥ prabhuḥ śeṣo 'nanto mahābhāgo duṣprakampyaḥ prakampitaḥ //
The thousand-headed serpent—Lord Śeṣa, the infinite Ananta—majestic and sovereign, bearing a banner like a golden palm, was stirred; he, who is ordinarily unshakable, became shaken.
It depicts a pralaya-like upheaval so intense that even Śeṣa-Ananta—normally described as unshakable—begins to tremble, signaling cosmic-scale disturbance.
Indirectly, it underscores impermanence and the need for dharma-based conduct: even the cosmic supports can be shaken, so kings and householders should rule/live with restraint, preparedness, and devotion rather than pride in stability.
While not giving a direct Vāstu rule, it contributes to iconographic visualization: Śeṣa/Ananta is marked as a thousand-headed nāga with a golden-banner motif—useful for pratīmā-lakṣaṇa (iconographic identification) in temple imagery.