Matsya Purana — Catalogue of the Eighteen Puranas
यो दद्यादयने कूर्मं हेमकूर्मसमन्वितम् गोसहस्रप्रदानस्य फलं सम्प्राप्नुयान्नरः //
yo dadyādayane kūrmaṃ hemakūrmasamanvitam gosahasrapradānasya phalaṃ samprāpnuyānnaraḥ //
A man who, at the time of the ayana (solstice), gives a tortoise in gift together with a golden tortoise image attains merit equal to the donation of a thousand cows.
This verse does not discuss pralaya directly; it focuses on dāna-dharma, teaching that properly timed and symbolically appropriate gifts yield vast spiritual merit.
It frames charity as a key duty: by giving prescribed gifts on sacred calendrical moments like ayana, a householder (and by extension a king) accrues merit comparable to major donations such as gifting a thousand cows.
The ritual significance is calendrical and symbolic: the ayana timing and the paired offering (tortoise plus golden tortoise image) indicate a rule-based, merit-amplifying dāna procedure rather than a Vāstu/temple-building instruction.