Matsya Purana — The Rite and Glory of Meru-Dāna: The Tenfold ‘Gift of Meru’ and Mountain-Offe...
स्वमन्त्रेणैव सर्वेषु होमः शैलेषु पठ्यते उपवासी भवेन्नित्यम् अशक्ते नक्तमिष्यते //
svamantreṇaiva sarveṣu homaḥ śaileṣu paṭhyate upavāsī bhavennityam aśakte naktamiṣyate //
In all such cases, the fire-offering (homa) is to be performed using only one’s own prescribed mantra; this rule is taught for the sacred hill-shrines. One should regularly keep a fast; but if one is unable, eating only at night is permitted.
This verse does not address pralaya; it focuses on ritual discipline—how to perform homa with one’s assigned mantra and what fasting observances are acceptable.
It frames a practical dharma for practitioners: perform homa according to one’s authorized mantra and maintain regular austerity (fasting), with a compassionate allowance (night-only meal) when full fasting is not possible.
Ritually, it specifies homa procedure and vrata (upavāsa/nakta) especially in śaila-kshetras (hill shrines), aligning temple worship with disciplined mantra-use and regulated diet.