What is ShiroVrata (a vow of holding fire on head)?
The Devī Bhāgavata Purāṇa has the description of a vrata by the same name.
On the rules of Śirovrata
1-43. Śrī Nārāyana said :-- The Brāhmanas that will perform duly the Śirovrata, to be described in the following, are the only ones who will attain very easily the highest knowledge, destroying all Avidyā or Ignorance. So much so that the rules of right living and right conduct as ordained in the Śrutis and Smritis are not necessary to be observed by those who duly and devotedly perform the Śirovrata (i.e., vow of the head; i.e., vow to apply ashes on the forehead). O Learned One! It is through this Śirovrata that Brahmā and the other Devas have been able to get their Brahmāhood and the Devahood. The ancient sages glorified highly this Śirovrata. Brahmā, Visnu, Rudra and the other Devas all performed this Śirovrata. O Wise One! Those that performed duly this Śirovrata, all became sinless though they were sinful in every way. Its name is Śirovrata, inasmuch as it is mentioned in the first part of the Atharva Veda. Only this vrata (vow) is called Śirovrata; no other thing is denominated by this name. By no other merit can this be acquired. O Muni! Different names are assigned to this vrata in different Śākhās; in fact, they are all one and the same.
N. B. -- Pāsupata vrata, Śivavrata, etc., are the different names assigned to it. In all the Śākhās, the One Substance, Intelligence solidified named Śiva and the knowledge thereof is mentioned. This is "Śirovrata." He who does not perform this Śirovrata, is irreligious and he is banished from all religious acts, though he is well-qualified in all branches of learning. There is no manner of doubt in this. This Śirovrata is like the blazing fire in destroying wholly the forest of sins. All knowledge fleshes before him who performs this Śirovrata. The Atharva Śruti expounds the subtle and particularly incomprehensible things; this Śruti declares the above Śirovrata as daily to be done; so it is one of the daily observances. "Fire is ashes," "water is ashes," "earth is ashes," "air is ashes," "ether or Ākāśa is ashes," "all this manifest Universe is ashes." These six mantras stated in the Atharva Veda are to be recited; after this, ashes are to be besmeared all over the body. This is named the Śirovrata. The devotee is to put on these ashes named Śirovrata during his Sandhyopāsanā (practising Sandhyā thrice a day); so long as the Brahmā Vidyā (the knowledge of Brahmā) does not arise in him. One is to make a Sankalpa (resolve) of twelve years before one starts with this Vrata. In cases of incapability, a period of one year or six months, or three months or at least twelve days are to be adopted. That Guru is considered very cruel and his knowledge will come to an end who hesitates and does not impart the knowledge of the Vedas and other things to him who is purified by observing this Śirovrata. Know him certainly as a very merciful Guru who illumines the heart by Brahmā Vidyā just as God is very merciful and compassionate to all the living beings. One who performs one's own Dharmas for many births, acquires particular faith in this Śirovrata; others can have no faith in this. Rather he gets animosity for this vrata, because of the abundance of ignorance in him. So one ought never to advise on spiritual knowledge to an enemy who has no faith, rather who has hatred for any such thing. Those only that are purified by the observance of Śirovrata are entitled to Brahmā Vidyā; and none others. So the Vedas command :-- Those are to be advised on Brahmā Vidyā who have performed Śirovrata. Even the animal becomes freed of his animalism, as a result of this vrata; no sin occurs in killing that animal; this is the decision of the Vedānta. It has been repeatedly uttered by Jāvāla Risi that the Dharma of the Brāhmanas is to put on the Tripundra (three curved lines of ashes on the forehead). The householders are instructed to put on this Tripundra by repeating the mantra "triyamvaka"' with Om prefixed. Those that are in the stage of the Bhiksus (Sannyāsis, etc.,) are to put on this Tripundra uttering thrice the mantra "Om Hasah." Such is regularly stated in Jāvāla Śruti. The house holders and the Vānaprasthis (foresters) are to put on this Tripundra, uttering Triyamvaka mantra purified with "Haum" the pranava of Śiva prefixed.
Here ends the Ninth chapter of the Eleventh Book on the rules of Śirovrata in the Mahāpurānam Śrī Mad Devī Bhāgavatam of 18,000 verses by Mahārsi Veda Vyāsa.
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