An asura (demon) called Bhasmasura was very strong and powerful but he was rather dumb. He once decided to do penance to seek a boon from Lord Shiva. So he meditated non-stop for a year and gradually kept on chopping off a part of his body to offer to Shiva as an offering. At long last, Lord Shiva was so touched and pleased with him that he appeared before Bhasmasura and asked him what he wanted.
Bhasmasura replied, ?I want the whole world. Please grant me the wish that on whosoever'shead I place my hand, he or she would die immediately.?
Lord Shiva agreed and granted the boon.
Bhasmasura was so thrilled that he went forward to try out his powers on Lord Shiva itself. Sensing his aim, Lord Shiva got such a fright of his life that he rushed towards Lord Vishnu for help with Bhasmasura following him, close on his heels.
Lord Vishnu immediately sensed that something was amiss and decided to change his form. As Bhasmasura was running, Lord Vishnu appeared before Bhasmasura in the garb of a priest. Lord Vishnu asked Bhasmasura, ?Why are you running at such speed as though there is a ghost chasing you? Why don'tyou stop and talk to me??
Bhasmasura stopped and told the priest about Lord Shiva'sboon and how Shiva was not letting him try his hand at testing the boon. At this Lord Vishnu replied, ?Why would Lord Shiva do this? I know that he did not allow you to keep your hand on his head because then you would have learnt that the boon he had granted to you was not true. On discovering that he had lied to you, you would not have spared him. So he was trying to escape from you.?
Bhasmasura was shocked and angry. He shouted in anger, ?But how can you be sure that what you know is correct??
Lord Vishnu, disguised as the priest, explained, ?If you do not believe me, then try the trick on yourself. Keep your hand over your head and you will find that nothing will happen. This way you will learn that Lord Shiva had told you a lie.?
Bhasmasura, foolish as he was, without thinking twice placed his hand over his head and perished instantly. It seems that is why it is said that angels fear to tread where fools reside.