Sri Rama Avatara is the seventh Avatara of Lord Vishnu. The story of Rama Avatara is also mentioned in Padma Purana’s Uttara Khanda.
Once, goddess Parvati expressed her desire to know about all the incarnations of Lord Vishnu.
Continuing with the various incarnations of Lord Vishnu, Lord Mahadeva told Parvati —
Describing about Sri Rama’s incarnation Lord Mahadeva told Parvati — ‘Once, Swayambhuva Manu had expressed his desire of having Lord Vishnu as his son to which Lord Vishnu had agreed.
During Treta Yuga Manu manifested himself as Dasharath and Vishnu kept his promise by taking birth as his son–Sri Rama. Similarly, during Dwapar Yuga Manu was born as Vasudev and Lord Vishnu kept his word by taking birth as his son–Krishna. After the completion of one thousand divine years, Manu will be born in the village of Sambhal as Harigupta and Vishnu will take birth as his son–‘Kalki’.
Lord Shiva then continued with the incarnation of Sri Rama and said–‘Sage Vishrava was the son of Pulasya and was married to Kekashi. Ravana and Kumbhakarna were born to the couple. Sage Vishrava also had a daughter named Shurpanakha and a virtuous son named Vibhishan. Ravana and Kumbhakarna did austere penance to please me (Lord Shiva). When I appeared before Ravana he requested the boon of immortality from me.
After receiving the boon, Ravana became very arrogant and started tormenting the inhabitants of all the three worlds. The deities became scarred and took the refuge of Lord Vishnu. Lord Vishnu assured them that he would solve their problem by taking incarnation as Sri Rama.
Dasharath came from the lineage of Surya. He had three queens—Kaushalya, Sumitra and Kaikeyi. Once, Dasharath performed a Vaishnav Yagya with the objective of acquiring a son. Lord Vishnu appeared and assured him that he would take incarnation as Sri Rama in a short time. Lord Vishnu gave a bowl of divine kheer to Dasharath, which he distributed amongst his three queens. In course of time, Kaushalya gave birth to Sri Rama on the auspicious day of Chaitra-Navami. The deities and the sages rejoiced at his birth.