Skanda Sashti is a very famous fast among the Hindu devotees. The story behind this famous fast goes as follows:
Once there lived a demon called Surapadma. Surapadma had received invincible powers from Lord Shiva. He began abusing his powers and terrorizing everyone. Unable to bear his torture, Gods and humans got together for prayer (Skanda Sashti Kavacham). During this time, to defeat Surapadma, Lord Shiva decided to give birth to a divine child inheriting all his powers and glory. Lord Shiva gave out six sparks from his third eye. The six sparks turned into six divine children. One day, Mother Parvati visited the children and in all her love embraced all of the children together. The six children became one with six faces, Arumugam (Lord Murugan). The prayer that the Gods and humans got together for lasted 6 days. On the 5th day, Mother Parvati presented Lord Murugan with a spear called Vel and was ordered by Lord Shiva to vanquish Surapadma. On the 6th day Lord Arumugam went to war against Surapadma. Surapadma tried tricking Lord Arumugam by disguising himself as other Gods and people, however, none of it worked. Finally, Lord Muruga defeated Surapadma turned him into a peacock and cock. The peacock became Lord Murugan’s vehicle and the cock attained a permanent place in Lord Murugan’s flag.
The event of killing the Surapadma is termed as Sura Samharam, which is famously celebrated in temples that are dedicated to Lord Murugan.