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Putrakameshti performed by King Dhasharatha-Rishyashringa performed the holy sacrifice and the final day of the event, a dark skinned deity appeared from sacrificial altar and handed over a vessel of payasam to Dasharatha.
Putrakameshti is a special Yajna performed in Hinduism for the sake of having a male child/son. It is a kaamya-karma.
In the Ramayana, upon the recommendation of Sage Vashishta, King Dasharatha of Ayodhya performed the Putrakameshti Yajna under the supervision of Rishishringa Muni, who was an expert in Yajurveda, which has the guidelines for this prayer. After its successful completion, the Lord of Fire, Agnidev appeared and gave a bowl of sweet to the King of Ayodhya, which was provided to his three queens in order to promulgate his sons Sri Rama, Lakshmana, Bharata and Shatrughna.