Matsya Purana — Bhīma-Dvādaśī
शिवस्य हृदये विष्णुर् विष्णोश्च हृदये शिवः यथान्तरं न पश्यामि तथा मे स्वस्ति चायुषः //
śivasya hṛdaye viṣṇur viṣṇośca hṛdaye śivaḥ yathāntaraṃ na paśyāmi tathā me svasti cāyuṣaḥ //
Viṣṇu dwells in the heart of Śiva, and Śiva dwells in the heart of Viṣṇu. Since I perceive no difference between them, may there be well-being for me—and long life as well.
It does not describe Pralaya directly; instead, it teaches theological non-difference (abheda) between Śiva and Viṣṇu, a principle used in Purāṇic tradition to establish cosmic harmony and auspiciousness.
By affirming non-sectarian reverence and inner unity, it supports dharma through social harmony—encouraging kings and householders to avoid divisive sectarianism and to cultivate auspicious conduct grounded in devotion and respect for multiple forms of the divine.
No direct Vāstu or iconographic rule is stated; ritually, the verse functions like a stotra/benediction (svasti) used to invoke auspiciousness and longevity through Hari–Hara unity.