Lord Shiva explained rati about rebirth of kamdev in form of Praduman and also the importance of the Anang Trayodashi. Devotees who observe this vrat will get happiness, wealth and marital bliss.
After the self immolation of Sati in the Yagya of Daksha Prajapati, lord Shiva got very disturbed. He carried her dead body on his shoulder and started traveling. To finish the illusion of Sati, lord Vishnu fragmented her dead body. Then, lord Shiva got engaged in meditation.
On the other side atrocities of demon Tarkasur were increasing day by day. He attacked on Devlok and defeated Devraj Indra. All God were upset about their condition. They approached Lord Brahma for help. Lord Brahma thought over it and said that only son of lord Shiva can kill Tarkasur. Hearing this, all of them got worried because Lord Shiva was meditating in grief of separation from Sati. Waking up lord Shiva and getting him married was next to impossible for all the Deities.
Kamdev decided to wake up Lord Shiva from from the trance. Kamdev succeeded and Samadhi of lord Shiva was broken. In turn, Kamdev lost his body. When all God told lord Shiva about Tarkasur, his anger came down and he realised his mistake.
Lord told Rati that kamdev is still alive but, he does not have a body. Lord Shiva asked her to wait till Trayodashi. He said, when Vishnu will take birth as Krishna, and then later Kamdev will be born as Praduman, son of Krishna.
How to Celebrate
Anang Trayodashi is a fast observed in respect to Lord Shiva.This Vrat is observed on Shukla paksha trayodashi of chaitra month. Usually this ritual is observed in Gujarat and Maharashtra. In north India, Anang Trayodashi observed on Margashirsha shukla Trayodashi. The rituals and puja procedures may differ slightly according to the region.
Anang Trayodashi fast is described in Garuda Purana. This vrat is observed throughout the year, i.e on every thirteenth day of the Shukla Paksha of each month. By observing Anang trayodashi Vrat will provide prosperity, health, wealth and good fortune.
During Anang Trayodashi vrat, devotees also worship Rati and Kama. During the puja people offer flowers and fruits to the God Shiva and perform Shodashopachara (16 step) puja. Grand celebrations will be performed at Kandarp Ishwar of Ujaain.
Kamdev is also known as Kandarp. Ujaain Kandarp Ishwar darshan is considered verymuch auspicious on this day. It is also belived that visiting this temple on anang trayodashi will attain moksha.