svarūpeṇa tathā vahnir nityaṃ dahanadharmakaḥ / upanītaṃ dahatyarthaṃ dāhyaṃ nānyan na cānyadā //
Though by its very nature fire is eternally of the nature of burning, it burns only what is brought near [to it], [and] only what is combustible, not anything else, nor at any other time.