In the famous Kaal Bhairava Ashtakam of Adi Shankaracharya we find the verse -
काशिकापुराधिनाथकालभैरवं भजे ॥७॥
To him whose loud laughter can tear asunder all born of the egg of the Brahma. That fierce ruler whose very sight to is enough to destroy the web of sins. To the granter of eight siddhis, the one one who wears a garland of skulls; I salute the Kaalbhairava, the Lord of the city of Kashi. verse 7
I want to know about the occasion or incident about which Adi ShankarAchArya is talking about. Can anyone provide the incident?