Once, Lord Krishna went to Kailash mountain to do penance with the desire of having a son. He found Maharishi Upamanyu engrossed in his meditation. He told Upamanyu about his desire and requested him to describe about the greatness of lord Shiva.
Upamanu described about his own experience when he had divine glimpses of lord Shiva who was meditating
“Once I saw Shiva who was surrounded by all the deities. Lord Shiva was engrossed in his deep meditation. Shiva had in his possession all the divine weapons like – Trident, Axe, Noose, Sudarshan etc. Lord Vishnu and Brahma were also present there. I eulogized lord Shiva who became pleased with me. Lord Shiva wanted to bless me with a boon. I requested lord Shiva to bless me with three things- 1) I should always remain his devotee 2) to be able to know about the past, present and future events, 3) My family should never feel the scarcity of rice and milk.”
“Lord Shiva not only blessed me with all these three things, but also to be able to see the
Vaivasvat kalpa.”
After completing his story, sage Upamanyu told Krishna he must worship lord Shiva if he was desirous of a son, because Lord Shiva can be pleased quite easily.