King Dasaratha was unhappy because he had no heir to the throne. One day, Sage Vashistha, asked the king to perform the Ashvamedha yajana.
Meanwhile, Ravana, had acquired the boon of immortality from Brahma, and was creating havoc in heaven and on earth. The gods appealed to Vishnu to get rid of him.
While the yajna was going on, a magnificent figure arose and gave King Dasaratha a bowl of payasam, a rice pudding prepared as an offering to the gods.
The king gave the payasam to each of his three wives - Kausalya, Kaikeyi, and Sumitra.
Soon, the queens gave birth to beautiful boys. Lord Rama, the reincarnation of Vishnu, was born to Kausalya; Bharat to Kaikeyi; and Laxmana and Shatrughna to Sumitra.