Matsya Purana — Soma
*ऋषय ऊचुः कथं गच्छत्यमावास्यां मासि मासि दिवं नृपः ऐलः पुरूरवाः सूत तर्पयेत कथं पितॄन् एतदिच्छामहे श्रोतुं प्रभावं तस्य धीमतः //
*ṛṣaya ūcuḥ kathaṃ gacchatyamāvāsyāṃ māsi māsi divaṃ nṛpaḥ ailaḥ purūravāḥ sūta tarpayeta kathaṃ pitṝn etadicchāmahe śrotuṃ prabhāvaṃ tasya dhīmataḥ //
The sages said: “How is it that on every Amāvāsyā (new-moon day), month after month, the king Purūravas, son of Ilā, goes to heaven? And, O Sūta, how does he perform the tarpaṇa (libations) for the Pitṛs, the Ancestors? We wish to hear of the extraordinary power and efficacy of that wise one.”
This verse does not discuss Pralaya; it introduces a ritual-ethical topic: the exceptional fruit (prabhāva) of Amāvāsyā observance and Pitṛ-tarpaṇa connected with King Purūravas.
It frames kingship and household duty around Pitṛ-kārya: regularly satisfying the ancestors through tarpaṇa—especially on Amāvāsyā—presented as a source of spiritual merit so great that Purūravas is said to attain heaven repeatedly.
The significance is ritual (not architectural): Amāvāsyā is highlighted as a recurring, high-efficacy time for Pitṛ-tarpaṇa, prompting an explanation of the correct procedure and its results.