Matsya Purana — Ekoddiṣṭa Śrāddha
दशाहं शावमाशौचं ब्राह्मणेषु विधीयते क्षत्रियेषु दश द्वे च पक्षं वैश्येषु चैव हि //
daśāhaṃ śāvamāśaucaṃ brāhmaṇeṣu vidhīyate kṣatriyeṣu daśa dve ca pakṣaṃ vaiśyeṣu caiva hi //
The period of death-related āśauca is prescribed as ten days for Brāhmaṇas; twelve days for Kṣatriyas; and for Vaiśyas, indeed, a fortnight.
This verse does not address Pralaya; it gives dharma-śāstra style rules on śāvāśauca (impurity after a death) and its duration by varṇa.
It regulates when householders (and rulers) may resume rites, offerings, and public duties after a death in the family/community, by specifying the mourning-impurity period for different social classes.
Ritually, it defines eligibility for worship, śrāddha-related observances, and other sacred acts during the āśauca window; it contains no Vāstu/temple-architecture instruction.