Matsya Purana — Śrāddha Procedure: Types
यस्मादन्नाद्धृता मात्रा भक्षयन्ति द्विजातयः अन्वाहार्यकम् इत्युक्तं तस्मात्तच्चन्द्रसंक्षये //
yasmādannāddhṛtā mātrā bhakṣayanti dvijātayaḥ anvāhāryakam ityuktaṃ tasmāttaccandrasaṃkṣaye //
Because the twice-born (dvija) partake of a measured portion taken from the cooked food, it is therefore called “anvāhāryaka”; hence this rite is performed during the waning of the moon.
This verse is not about Pralaya; it explains a ritual term (anvāhāryaka) and specifies its proper lunar timing during the waning moon.
It supports gṛhastha-dharma by prescribing how offerings/food portions are to be set aside and given for ritual consumption by qualified dvijātis, and by fixing the observance to the waning lunar phase.
Ritual significance: it defines ‘anvāhāryaka’ as a measured portion taken from prepared food and links the rite to candra-saṃkṣaya (the moon’s waning), indicating precise calendrical discipline in performance.