Birth of Budha
Once Chandra (चन्द्रमा) visited the house of Brihaspati (बृहस्पति) the Guru and instantly fell in love with his wife Tara (तारा), who too reciprocated her romantic feelings. In course of time, Tara deserted Brihaspati and moved into Chandra’s house. Brihaspati approached Chandra and counselled him that this romance with his own Guru’s wife was not only illegitimate but a sin equal to ‘Brahma Hatya (ब्रह्म हत्या)’ and asked Tara to be returned to him.
Chandra declined to do so as Tara came on her own desire. Brihaspati approached Indra asked for his help, who dispatched an emissary to Chandra. The emissary advised Chandra to be sensible as he already had twenty eight beautiful wives and even offered any of the Apsaras. The Messenger returned to Indra empty handed and the latter decided to wage a war against Chandra.
Knowing of this incident, the Guru Sukracharya, the arch-rival of Devatas went to Chandra and assured him of help in a possible war. Meanwhile Brahma approached and asked Chandra & Sukracharya to end this war and return the wife of Brihaspati, than Chandra let Tara return to Brihaspati.
After coming from Candra’s house Tara gave birth to boy, and confirmed that he was Chandra’s son. Chandra took away the child and named him as Budha (बुध).
Story of Ila and marriage to Budha
Once there was a King named as Sudyumna (सुद्युम्न), who went for hunting and during the course of hunting he went into a forest called as “Kumar”. The moment he went in to the forest along with his ministers and solders, they all got converted as women.
This happened due to a spellbound of Lord Siva that anyone who enter that forest will turn into a woman. Once Lord Shiva and PAravati’s privacy was disturbed by few sages who entered in the forest. Due to which when King Sudyumna enters it , he turn into a women.
The King thus converted into a woman was known as Ila (इला), who out of shyness did not return to the Kingdom. Soon Budha met Ila and they were married and had a child, named Pururava (पुरुरवा)
Meanwhile Ila met Sage Vasishtha and revealed the entire happening and the Sage prayed to Lord Siva and begged Him a way out for the pious King Sudyumna to get back his original position. Lord Siva agreed to let Ila attain manhood every alternate month. Thus the appearances of Ila and the King alternated every month and as the wife of Budha, Ila gave birth to Pururava. When Pururava was made the King, Sudyumna retired to Vanasprastha.
Pururava when took over the kingdom of King Sudyumna, he was called as first king of Lunar Dynasty (Chandravanshi)