Story of Ganga descending to Earth by Bhagiratha's Prayers

Once the king of Ayodhya, King Sagara, was worried as he had no heirs. Along with his two wives, he went to Mount Kailash to perform severe penances. Soon, Lord Shiva appeared before them and blessed the king. He said, “You shall have sixty thousand sons from one wife, but they will all perish. Your other wife will have one boy, but his descendants will bring glory to your dynasty.”

The king, with his queens, returned to kingdom. As predicted, one queen gave birth to sixty thousand sons, who grew up to be very brave warriors. The other queen gave birth to one son who grew up with his brothers to be a warrior like them.

After a few years, King Sagara decided to conduct the Ashwamedha yagna (ritual sacrifice) to expand his kingdom. It was a ritual where a horse was released to wander for a year and the kings of all the kingdoms where the horse wandered were asked to submit to his rule or face war. Lord Indra, the King of the Devas, grew concerned as he feared that the horse will easily defeat him. Therefore, he stole the ceremonial horse and tied it outside Sage Kapila’s ashram.

When the horse could not be found, King Sagara sent his sixty thousand sons to find the horse. They turned the earth inside out in search for the horse. Finally, they reached Sage Kapila’s ashram and found it. Assuming that the Sage had stolen the horse, they threatened him, who was meditating. The Sage opened his eyes and burned the princes to ashes with one glance.

Anxious King Sagara, sent his grandson Anshuman to search for his uncles. He found the horse and his uncles’ ashes outside Sage Kapila’s asharam. He politely enquired about his uncles’. Sage Kapila was impressed by his humility and said, “They committed a fatal mistake. Only the purifying water of Goddess Ganga will help them attain heaven.” A distraught Anshuman returned to King Sagara to deliver the news. The king was devastated by the news and decided to perform severe penance to Goddess Ganga. He passed away before his wish could be granted.

Anshuman succeeded King Sagara on throne, who was then followed by his grandson, Bhagiratha. Bhagiratha, like his grandfather and great-grandfather, performed severe penance to Goddess Ganga to fulfill his familial duties. Goddess Ganga heard his prayer but feared that her strong currents will wash away even the strongest gods. Lord Shiva assured her that he will see to it that her currents be tamed, and wound her up in his matted locks. But, not one drop of water fell on earth.

You can read more on the story at
http://www.kidsgen.com/fables_and_fairytales/indian_mythology_stories/descent_of_ganga.htm