The story of Hartalika Teej Vrat celebrated on Tritiya Tithi of Shukla Paksha of Bhadrapada month is as follows-
According to a legend in the Linga Purana, mother Parvati, in her former birth, meditated in her childhood on the banks of the Ganges on the Himalayas to obtain Lord Shankar as her husband. During this time he did not consume food. They spent a lot of time chewing dried leaves and then spent many years drinking only air. His father was extremely sad to see this situation of Mother Parvati.
Meanwhile, one day Maharishi Narada approached Parvati's father on behalf of Lord Vishnu with the proposal of marriage of Parvati ji, which she accepted with pleasure. When the father told his mother Parvati about their marriage, she became very sad and started mourning loudly. Then on the request of a Sakhi, Mother told her that she is doing this harsh fast to get Lord Shiva as husband while her father wants to marry her to Vishnu. Then on the advice of Saheli, Mata Parvati went into the dense forest and went to a cave and got absorbed in the worship of Lord Shiva. (Learn more about Parvati ji: Mahashakti Mata Parvati)
On the day of Bhadrapada Tritiya Shukla, Hath Nakshatra was built by Shiva with sand by Mata Parvati and immersed in the praise of Bholenath and awakened the night. Pleased with this harsh penance of Mother, Lord Shiva appeared to her and accepted her as his wife at will.
It is believed that on this day, women who perform this fast lawfully and with full devotion, get a husband according to their mind. Also, this festival is also celebrated with the aim of maintaining happiness in married life. In many states of North India, it is customary to apply henna and swinging on this day.