King Dasaratha performs the Aswamedha yaga to beget sons. It is decided that the rituals will take place on the northern bank of the Sarayu river, and preparations for the yaga begin. Dasaratha also informs his queens of the yaga, so that they can also adhere to the required observances. Sumantra, a minister in Dasaratha's court, extols the virtues of sage Rishyasringa, son of sage Vibhandaka, and the son-in-law of King Romapada. Sumantra narrates how the birth of Dasaratha's sons had been predicted by none other than sage Sanatkumara. Dasaratha requests Romapada and Rishyasringa to be present at the time of the yaga.
Romapada and Rishyasringa are duly welcomed into Ayodhya, and the yaga is performed. In the meantime, Lord Vishnu decides that it is time to incarnate as a human being in order to slay Ravana. Ravana had obtained from Brahma a boon, as a result of which none other than a human being could kill him. The Lord chooses Dasaratha as His father.
King Dasaratha, having performed the Aswamedha yaga, also performs the Putrakameshti yaga to have progeny. Out of the sacrificial fire comes a divine being, who is dazzling. He holds a golden vessel with a silver lid. He tells Dasaratha that he should give the porridge in the vessel to his wives, and they will then give birth to sons. Dasaratha approaches Kausalya first, since she is the chief queen. He gives her half of the porridge. He gives Sumitra a quarter and Kaikeyi one-eighth. The remaining portion he gives again to Sumitra. As a result, Kausalya gives birth to Rama, Kaikeyi to Bharata, but Sumitra who receives two helpings gives birth to Lakshmana and Shatrugna.
King Bhoja gives a version of this part of this story, which differs from Valmiki's, but is nevertheless interesting, said Vaduvur Veeraraghavachariar. His version says Kausalya was first given half, she being the chief queen, and then Kaikeyi was given the remaining half. This left out Sumitra. The other two queens were sorry to see Sumitra having been excluded thus. So they gave her half of each of their portions. And they did so voluntarily, showing the goodwill Dasaratha's wives had for one another.