Matsya Purana — Kṛṣṇāṣṭamī Vrata: Monthly Śiva-Names
न वित्तशाठ्यं कुर्वीत कुर्वन्दोषमवाप्नुयात् कृष्णाष्टमीमुपोष्यैव सप्तकल्पशतत्रयम् पुमान्सम्पूजितो देवैः शिवलोके महीयते //
na vittaśāṭhyaṃ kurvīta kurvandoṣamavāpnuyāt kṛṣṇāṣṭamīmupoṣyaiva saptakalpaśatatrayam pumānsampūjito devaiḥ śivaloke mahīyate //
One should not practice deceit in matters of wealth; whoever does so incurs fault. But by fasting on Kṛṣṇāṣṭamī alone, a man—honoured and worshipped by the gods—attains great eminence in Śiva’s world for an immeasurably long divine span, as though for hundreds of kalpas.
This verse does not discuss Pralaya; it focuses on ethical conduct (avoiding financial deceit) and the long-lasting merit gained through fasting on Kṛṣṇāṣṭamī.
It frames a core duty for householders and rulers alike: do not engage in financial fraud. Wealth acquired or handled through deceit is treated as doṣa (moral fault), while disciplined vrata-observance (like fasting on Kṛṣṇāṣṭamī) is praised as a purifier and merit-generator.
The significance is ritual (vrata): observing an upavāsa (fast) on Kṛṣṇāṣṭamī is said to yield extraordinary spiritual reward—honour by the gods and exaltation in Śivaloka—rather than any Vāstu or temple-construction rule.