This fast is undertaken in Magh Shirish Krishna Ashtmi. Bhairav is a manifestation of Lord Shiva in his Rudra form; the dreadful form, from which even death (Kaal) fears. The fast, undertaken on this day, is fruitful, believed to be a protection from direct and indirect obstacles in life. Bhairav's conveyance is a dog.
Bhairav (Shiva) is worshipped in the temples. His carrier Dog is fed with milk, curd and sweets.
Once, there was a controversy between two Gods Brahma and Vishnu. The point of difference was as to who, of the two, is superior. To decide the issue, saints, rishis and sages were summoned, who after deliberations pronounced that in fact there is a special power, Brahma and Vishnu are forms of the same. Vishnu was satisfied but Brahma could not agree with the judgment of the jury. Lord Siva could not tolerate this defamation of the jury; he instantly appeared in the form of Bhairav and smashed the pride of Brahma.
This day and the fast thereon, in reverence to Bhairav, who is kind to his devotees and saves them from the havoc of time (Kaal).