Matsya Purana — Vishnu’s Battle with Mathana
ततो व्यावृत्य वदनं महाचलगुहानिभम् ग्रस्तुमैच्छद्रणे दैत्यः स गरुत्मन्तमच्युतम् //
tato vyāvṛtya vadanaṃ mahācalaguhānibham grastumaicchadraṇe daityaḥ sa garutmantamacyutam //
Then, turning his face—like a cavern in a great mountain—the Daitya, in the midst of battle, sought to swallow Garuḍa and Acyuta (Viṣṇu) together.
This verse does not describe Pralaya; it uses cosmic-scale imagery (a mouth like a mountain-cave) to intensify a battlefield moment where a Daitya attempts to devour Garuḍa and Acyuta.
Indirectly, it models the Purāṇic theme that adharma (violent, predatory arrogance) is self-defeating when directed against dharma’s protectors (Viṣṇu/Acyuta); kings are repeatedly urged in the Matsya Purāṇa to restrain such cruelty and uphold righteous conduct in conflict.
No Vāstu or ritual rule is taught here; the phrase “like a cave in a great mountain” is a poetic simile, though it can be cited in literary studies of Purāṇic spatial imagery rather than temple architecture prescriptions.