Matsya Purana — Vrata-Ṣaṣṭhī: The Sixty Sacred Vows
दद्याद्द्विकालवेलायां प्रीयेतां शिवकेशवौ दत्त्वा परं पदं याति सौम्यव्रतमिदं स्मृतम् //
dadyāddvikālavelāyāṃ prīyetāṃ śivakeśavau dattvā paraṃ padaṃ yāti saumyavratamidaṃ smṛtam //
One should make the offering at the two daily junctures (morning and evening); then Śiva and Keśava are pleased. Having given thus, one attains the supreme state—this is remembered as the Saumya-vrata.
This verse does not discuss pralaya directly; it teaches vrata-dharma—how timed offerings at dawn and dusk please the deities and lead toward the supreme goal.
It prescribes a practical discipline for daily life: making offerings at the two sandhyā-like times. Such regulated giving and worship is presented as a dharmic duty that supports spiritual merit and liberation.
The ritual significance is the timing: offerings should be made at the two daily junctures (morning/evening), emphasizing correct kāla (ritual time) as a key rule in Purāṇic practice.