Lord Shiva, with his third eye, burnt the cupid (Kamadev) into ashes. As the cupid was consumed by fire, it had to be reborn from fire. (back story)
After a few years, King Brihadrava, of the Janamejaya dynasty, of Kuruvamsa, decided to do Soma- Yagya.
Soma- Yagya is a kind of sacrifice which is done in the presence of fire. Soma-Yagya gets its name from the “Soma juice”, which is used as the main oblation in this Yagya.
Soma is a great medical herb and is also called the “King of Medicinal Herbs”. Soma-Yagya is done because it adds an extra powerful boost of healing energy into the atmosphere.
King Brihadrava performed the Soma-Yagya. When the Yagya was over, the Brahmins put their hands into the Yagya to collect ashes from the fire pit. But, to their surprise, instead of the ashes, they had a crying child in their hands.
The king was happy to see the child and gave the child to his queen. She was also happy to have another child and they considered him to be a gift from the fire god.
As it was gifted by the fire god they named the child “Jalandar”.
When he grew up, his parents started looking for a girl for Jalandar’s wedding. But all this did not feel right to Jalandar and so he left home.
And from here on, Jalandar’s spiritual life began. Jalandar ran away from home and stayed in the forest.
When Jalandar was fast asleep, the forest caught fire. The fire god realized that this was his son and woke up Jalandar. The fire god told him the story of his birth and brought him to Lord Dattatreya.
Lord Dattatreya trained Jalandar for the next 12 years to enlighten him. The Lord then preached the special mantra in his ear.
It is believed that the moment the mantra touched Jalandar’s ear his ignorance vanished and he attained spirituality.
He became a member of the “Nath Sect” and was called “Jalandarnath”.