Bhagiratha Propitiates Shankara for the Boon
Having learned that only Maheshvara can bear the force of Ganga's descent, Bhagiratha travels to Mount Kailasa and begins a new round of austerities. He does not stop until Shankara himself grants the boon: the god will bear the river on his head, so that Bhagiratha's fathers may finally reach heaven.
Bhagiratha had spent a thousand celestial years in austerity to bring Ganga to earth. She had agreed to come. But she had also told him the truth: her descent would shatter the world unless someone bore her force.
That someone was Shankara — Maheshvara, the great god, the blue-throated one who had once drunk the poison that would have destroyed the universe. Only he could withstand the weight of a heavenly river falling from the sky.
So Bhagiratha went to Mount Kailasa.
Kailasa is the mountain of the gods, the place where Shankara sits in meditation with his consort Parvati, the place where the Ganga herself flows through his matted hair in the form of a goddess. It is not a place one simply visits. It is a place one earns.
Bhagiratha began his austerities again.
The text does not describe what he did on Kailasa — how long he stood, what he ate, what he endured. It says only that he satisfied Shankara through austerities, and that after some time had passed, he obtained the boon he sought.
The boon was this: Shankara would bear Ganga on his head.
When the river fell from heaven, she would land on the god's head first — her immense force broken by his matted hair, her waters slowed and tamed before they reached the earth. The world would not be destroyed. The river would flow.
And Bhagiratha's fathers — the sixty thousand sons of Sagara, reduced to ash by Kapila's energy, trapped in Yama's realm for want of a single touch of sacred water — would finally be entitled to reside in heaven.
Bhagiratha had done what no one else could do. He had moved a river and a god. Aranyaka Parva, Chapter 404