ahush had six sons- Yati, Yayati, Sanyati, Ayati, Viyati and Kriti. Yayati had two wives, Devyani, the daughter of Shukracharya and Sharmishtha, the daughter of Vrishparva. Devyani gave birth to Yadu and Turvasu whereas Sharmishtha gave birth to Druhayu, Anu and Puru. Because of a curse of Shukracharya old age had descended on Yayati prematurely.
Yayati then requested his eldest son Yadu to exchange his youth with his old age but Yadu refused. Then Yayati requested each of his sons one by one but all of them refused plainly for the fear of getting old prematurely.
At last Yayati’s youngest son Puru gladly accepted his request and gave him his youth. Regaining the youth, Yayati once again indulged in carnal pleasures with both his queens. But everyday his desire for pleasures increased like a fire flared up by ghee. After one thousand years Yayati realised his mistake and decided to expiate for his sin. Thus, Yayati returned Puru his youth and acquired his old age once again. Then crowning Puru as the king, he took an exile to the forest.