Shiva , the Digambaraaya is beyond the worldly affairs, so smears ash on His body and wanders through out the Universe.
According to Shiva Puran- Lord Shiva used to wander around the forests bare bodied. There was a forest by the name Daruka which was home to various sages, who used to stay there along with their families.
The Rishi wives had utmost loyalty to their husbands , and always followed Pativratha dharma.
One day, Mahadev enters this forest.
The Rishi wives seeing the Handsome Shiva, fell in love with Him. Shiva , the Bholenath doesn’t even look at them, and leaves from that place. After travelling for sometime, Shiva sits under a tree and starts to meditate.
Meanwhile, the wives of the Sages ,constantly thinking only about Handsome Shiva ,could not concentrate on their daily routines / household chores.
The saints with their powers, figure out the reason behind their wives changed behavior, is none other the Shiva (the naked Aghori ) and decide to teach him a lesson.
The next day, the saints see Shiva walking in the forest, so they dig a huge pit on the same way. And the sages perform a Yagna and as the Yagna’s output, a tiger emerges from the pit and plunged on Shiva !
Shiva within a second, killed the tiger and tore off its skin and draped it around his body. Seeing the mighty Shiva, it didn’t take much time for them to realize that the man is no ordinary.
All the sages fell on Shiva’s feet.
From that day , Shiva wears the tiger skin to show that He is all powerful, He is Pashupathi nath and above the animal instincts.