The legend of Gangas descent from the heavens into the earth has been narrated in the Hindu mythological epic of Ramayana. The legend explains the popular custom of giving bath to Shiv Linga on Shivaratri festival.
Once King Sagar - the ruler of Ayodhya and an ancestor of Lord
Rama successfully performed the Ashwamedha Yagya for 99 times. Each
time, he sent the horse around the earth it returned to the kingdom
unchallenged. However, Indra - the King of Gods became jealous of
King Sagars success. So when King Sagar performed the sacrifice of
the 100th time, Indra kidnapped and hid the Yagya horse in the hermitage
of Kapila Muni
In search of the horse, sixty thousand princes from Ayodhya reached
Kapil Munis hermitage. They mistook the sage to be the abductor
and attacked him. An enraged Kapila Muni burnt the 60,000 princes to
ashes. On hearing about the plight of his father and uncles, King
Bhagiratha - one of the grandchildren of King Sagar requested Kapila
Muni to grant a solution to the problem. Kapila Muni advised that the
waters of the river Ganga would miraculously bring back the dead princes
King Bhagirath left his kingdom and began to mediate
for the salvation of the souls of his ancestors. It is said that
Bhagirath observed a penance to Brahma for a thousand years, requesting
Ganga to come down to earth from heaven and wash over his ancestor's
ashes to release them from a curse and allow them to go to heaven.
Pleased with the devotion, Brahma granted Bhagiraths wish but told
him to pray to Lord Shiva, as he alone could sustain the weight of her
Accordingly, Lord Shiva held out his thick matted hair to catch the
river as she descended. The meandering through Shivas lock
softened Gangas journey to the earth and the holy waters of river
Ganga thus washed away the ashes of Bhagiraths ancestors. A
modified version of the legend says, what reached the earth were just
sprinkles from Lord Shivas hair. The Ganga, thus, became an
attribute of Shiva. This manifestation of Shiva is known as Gangadhara.
The legend is re-enacted by devotees of Lord Shiva as they give a bath
to the linga during worship. And for this reason, many devotees prefer
to take a dip in the holy water of river Ganga on a Shivaratri day.