Matsya Purana — Manvantaras
त्रयोदशैते विज्ञेया ब्रह्मिष्ठाः कौशिका वराः अगस्त्यो ऽथ दृढद्युम्न इन्द्रबाहुस्तथैव च //
trayodaśaite vijñeyā brahmiṣṭhāḥ kauśikā varāḥ agastyo 'tha dṛḍhadyumna indrabāhustathaiva ca //
These thirteen are to be known as the foremost, Brahman-realized sages among the excellent Kauśikas—namely Agastya, as well as Dṛḍhadyumna, and likewise Indrabāhu.
This verse does not discuss Pralaya; it functions as a genealogical/catalogue statement identifying a set of thirteen Brahman-established sages within the Kauśika lineage.
Indirectly, it supports the Purāṇic ideal that rulers and householders should honor and seek guidance from brahmiṣṭha sages—those established in Brahman—since such lineages preserve dharma, ritual correctness, and ethical counsel.
No Vāstu or temple-building rule is stated here; the ritual takeaway is the emphasis on brahmiṣṭha rishis as authoritative transmitters of sacred knowledge and proper practice.