Matsya Purana — Genealogy and Classification of Sacred Fires
हृदयस्य सुतो ह्यग्नेर् जठरे ऽसौ नृणां पचन् मन्युमाञ्जठरश्चाग्निर् विद्धाग्निः सततं स्मृतः //
hṛdayasya suto hyagner jaṭhare 'sau nṛṇāṃ pacan manyumāñjaṭharaścāgnir viddhāgniḥ satataṃ smṛtaḥ //
Indeed, this fire—born from the heart’s fire—abides in the belly; it cooks (digests) the food of human beings. Therefore this abdominal fire, endowed with forceful energy, is remembered as the ever-awake, ever-kindled fire.
This verse is not about cosmic pralaya; it describes the microcosmic “fire” within the human body—how the heart-derived fire becomes the digestive fire in the belly.
It implies that sustaining jatharagni through disciplined diet and conduct is part of self-governance; a householder (and a king) should preserve bodily strength and clarity by maintaining proper digestion and moderation.
No direct Vastu or temple-architecture rule is stated; the ritual takeaway is symbolic—Agni is ‘ever-kindled’ within, supporting purity and readiness for rites through bodily balance.