Matsya Purana — Genealogy of the Śūra–Vasudeva
प्रथमा या अमावास्या वार्षिकी तु भविष्यति तस्यां जज्ञे महाबाहुः पूर्वं कृष्णः प्रजापतिः //
prathamā yā amāvāsyā vārṣikī tu bhaviṣyati tasyāṃ jajñe mahābāhuḥ pūrvaṃ kṛṣṇaḥ prajāpatiḥ //
That new-moon day (amāvāsyā) which becomes the first annual observance—on that very occasion, in ancient times, the mighty-armed Prajāpati known as Kṛṣṇa was born.
It points to cosmogony through sacred time: a specific Amāvāsyā is linked with the birth of Prajāpati (a progenitor/creator figure), emphasizing creation emerging in ritually marked time rather than describing dissolution.
By identifying an annually significant Amāvāsyā, it supports dharma-based timekeeping: householders (and kings who regulate public rites) are to observe proper tithi timing for ancestral, purificatory, and calendrical rites aligned with scriptural authority.
The ritual takeaway is calendrical: this verse elevates a particular annual Amāvāsyā as especially sacred, implying heightened efficacy for Amāvāsyā observances (vrata/śrāddha-like rites), though it does not give Vāstu or temple-building rules directly.