The katha of Hartalika
From childhood Mata Parvati had resolved to win Lord Shiva as her husband and was doing harsh penance on the Himalaya. One day Narad Muni came and told King Himalaya that Lord Vishnu wished to marry his daughter. Himalaya happily agreed.
When Parvati ji learned of this she was very sad, for her heart was set on Shiva ji. She told her friends of her distress.
The friends thought of a plan and, hiding her from her father, took Parvati ji to a cave in a dense forest. Because she was carried away by her friends, this vrat came to be called 'Hartalika'.
On Bhadrapad Shukla Tritiya, in Hasta nakshatra, Parvati ji made a Shivling of sand in the cave, fasted without food or water and stayed awake all night singing bhajans of Shiva ji.
Pleased by her penance, Shiva ji appeared and asked her to ask for a boon. Parvati ji said, 'Accept me as your wife.' Shiva ji said 'Tathastu' (so be it). Later King Himalaya, searching for Parvati ji, also arrived there and agreed to her marriage with Shiva ji.
Vrat niyam
This is a nirjala vrat — not even water is drunk all day and night. There is a jagran at night and the vrat is broken the next morning after the puja. Images of Shiv-Parvati and Ganesh are made from sand or clay and worshipped.
This is OmKiran Bhakti's retelling of the traditional katha in simple English; details of the katha vary slightly from region to region.