[686] And what, bhikkhu, is the fire element (tejodhātu)? The fire element may be internal or it may be external. And what, bhikkhu, is the internal fire element (dhātu)? Whatever internally, belonging to oneself, is fire, fiery, and appropriated (upādinna) — that is to say: that by which one is warmed, that by which one is aged, that by which one is consumed with heat, and that by which what is eaten, drunk, chewed, and tasted comes to complete digestion — or whatever else internally, belonging to oneself, is fire, fiery, and appropriated: this, bhikkhu, is called the internal fire element. Now both the internal fire element and the external fire element are simply the fire element. That should be seen as it really is with right wisdom thus: "This is not mine, this I am not, this is not my self." Having seen it thus as it really is with right wisdom, one becomes disenchanted with the fire element and detaches the mind (citta) from the fire element.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.