Matsya Purana — Description of the Akṣaya Tṛtīyā Observance
वैशाखशुक्लपक्षे तु तृतीया यैरुपोषिता अक्षयं फलमाप्नोति सर्वस्य सुकृतस्य च //
vaiśākhaśuklapakṣe tu tṛtīyā yairupoṣitā akṣayaṃ phalamāpnoti sarvasya sukṛtasya ca //
Whoever observes a fast on Tṛtīyā, the third lunar day, in the bright fortnight of Vaiśākha attains an imperishable reward—the unfailing fruit of all meritorious deeds.
Nothing directly—this verse focuses on vrata (fasting) in Vaiśākha and the doctrine of akṣaya (imperishable) merit, not on pralaya cosmology.
It prescribes a practical dharma for householders (and rulers as exemplars): observing a calendrical fast (Vaiśākha Śukla Tṛtīyā) that is said to yield lasting spiritual merit, reinforcing discipline, charity-oriented piety, and public religiosity.
Ritually, it highlights upoṣa on a specific tithi as a high-yield observance (akṣaya-phala). No Vāstu or temple-construction rule is stated in this verse.