Chapter 28 of 76 · Vayaviya Samhita · Overall chapter 416 of 464
Nature of Bhasma
Prompted by Shiva's own remark to Devi about the universe having 'Agnishoma' as its atman, Vayu unpacks this into an extended meditation on bhasma (sacred ash) as Agni's energy flooded and tempered by Shakti-Soma's amrita, concluding that bathing in bhasma with the right mantra and understanding is itself a means to conquer death.
The rishis asked
What was it that Deva said to calm Devi? What does it mean that the universe has Agnishoma as its self? He also said that a command is the essence, and that she is the command behind his powers. We want to understand these things clearly and in sequence.
Vayu answered
Rudra's body is fierce and made of energy, and this is what is called Agni. Shakti is Soma, full of amrita, and her body is the one that brings peace. Amrita is Pratishtha. Tejas is Vidya and also Kala. Rasa and Tejas are present in all the subtle elements. Tejas acts in two ways, as the sun and as fire. Rasa too acts in two ways, in the moon and in water. Tejas lives in lightning and the like, Rasa in sweet things. Through the balance of Tejas and Rasa, all that moves and all that stays still is kept alive. Amrita comes from Agni and amrita makes Agni stronger. So the power of Agnishoma serves the whole world. Abundant grain grows for oblations, rain makes the grain grow, so oblations depend on rain, and Agnishoma thereby supports the universe.
Agni burns upward until it meets the supreme amrita of Soma. The amrita of Soma pours downward until it reaches the root of Agni. This is why Kalagni is below and Shakti is above. The rising flame goes on until everything has been burnt, and the falling stream goes on until everything has been drenched. Shakti is the foundation that holds up Kalagni as it climbs. Equally, the stream falling from Soma rests on Shiva's Shakti beneath it. Shiva is above and Shakti below; when Shakti is above, Shiva lies below her. So nothing exists that Shiva and Shakti do not fill.
At times Agni burns the universe and leaves only ash. Ash is called the energy of Agni, since it is nothing but that energy. A person who understands what ash is, and who bathes in it saying "Agni is this ash," is released from bondage. When ash is soaked in Soma but the two stay apart, the case is said to belong to Prakriti. When the ash is joined with it and soaked on all sides, Shakti pours down amrita and gives up that claim. This soaking in amrita is always what overcomes death. Whoever touches the amrita of Shiva and Shakti, how could he die? One who knows the secret of burning and soaking, as it has been described, leaves the state of Agnishoma and is never born again. Whoever burns his body in Shiva's fire and drenches himself in amrita from Shakti-Soma is ready for immortality. Keep in your heart what Deva said: everything that moves in the universe has Agnishoma as its self.
Retold in our own words from Bibek Debroy's English translation of the Shiva Purana (Penguin Classics). Names, numbers and the order of events follow the source.