Matsya Purana — Procedure for Going to Prayaga and the Greatness of the Ganga
ब्रह्मचारी जितक्रोधस् त्रिरात्रं यदि तिष्ठति सर्वपापविशुद्धात्मा सो ऽश्वमेधफलं लभेत् //
brahmacārī jitakrodhas trirātraṃ yadi tiṣṭhati sarvapāpaviśuddhātmā so 'śvamedhaphalaṃ labhet //
If a celibate student (brahmacārin), having conquered anger, maintains the observance for three nights, he is purified of all sins and attains the merit of an Aśvamedha sacrifice.
This verse does not discuss pralaya; it teaches moral purification through brahmacarya and control of anger, presenting an austerity whose merit equals an Aśvamedha.
Though framed around a brahmacārī, the principle applies broadly: self-restraint, especially mastery over anger, is praised as producing great merit—an ethical ideal relevant to rulers (for just governance) and householders (for disciplined conduct).
Architectural (vāstu) rules are not mentioned; the ritual point is that a short, disciplined observance of three nights with brahmacarya and krodha-jaya is credited with Aśvamedha-level merit.