Kartikeya was born to slay the demon Tadkasur who got the boon of getting killed by the son of Shiva only. Kartikeya killed and ended the terror of Tadkasur.
Kartikeya was a brave warrior but he always felt restlessness and confusion. He thought that his parents Shiva and Parvati don’t love him like they love Ganesha. He could easily be agitated by provoking.
Lord Vishnu discussed with him the reasons for such emotional upheaval. He told him that this was because of the effect of killing a devotee of Shiva. Although Tadkasur was an evil demon and Kartikeya was destined to slay him but he was none the less a great devotee of Shiva. So Kartikeya was suffering from the sin of killing a devotee.
Austerity by Kartikeya
To get relieved from the sin, Kartikeya wished to pray Lord Shiva and made a Shiva Linga by carving a stone.
As soon as he was about to pray, an old man came there and asked if he could give him his Shiva Linga for prayer. Kartikeya agreed and gave him the Shiva linga he made.
Both Ganesha and Kartikeya went on the search of finding another stone. They found one and carved to form a Shiva Linga. The same old man came once again and told that when he was carrying the previous Shiva Linga, it dropped from his hands. Kartikeya gave him his newly created Shiva Linga once again.
Kartikeya once again started his search for an appropriate stone. This time they found a yaksha guarding stones. He warned them not to touch any stone without his permission.
Kartikeya requested the yaksha to let him have one stone but he refused. He asked few questions and Kartikeya managed to answer them all correctly. Yaksha happily gave him a beautiful stone.
Kartikeya carved and made a Shiva Linga. He found the old man at his prayer place. He again happily offered his Shiva Linga which he made with extreme difficulties and after going through the test of Yaksha.
The old man turned into Shiva. He blessed him with freedom from the sin and enlightened him the requirement and importance of the tests he took of him.
Shiva named the first Shiva Linga Pratikeshwar, second Kapileshwar and the third one as Kumareshwar. All sins are relieved of those who pray at Kumareshwar Linga.