The Mahabharata says King Yayati passed over four sons who refused to take his old age, and made the youngest his heir

The Adi Parva says King Yayati was cursed with old age by the sage Shukra, the father of his queen Devayani, after his affair with her attendant Sharmishtha. The curse allowed him to pass his old age to a son. He asked each in turn. Yadu, the eldest, refused, and Yayati cursed him that his children would never be kings. Turvasu, Druhyu and Anu refused, and each was cursed. Puru, the youngest, Sharmishtha's son, agreed. He took his father's old age and gave him his youth. After a thousand years Yayati gave Puru back his youth and announced, "Therefore shall the youngest be my heir." The Brahmins and the four orders of society objected: how could the youngest be crowned over the eldest? Yayati answered that "he is no son who disobeyeth his father." The people agreed, and Puru was installed. Yayati went to the forest. The text names Yadu's descendants the Yadavas, Krishna's people. Puru's line became the Kurus, the dynasty of the Mahabharata war.