Anala, Anila, Soma, Ahas, Dhara, Dhruva, Pratyoosha, and Prabhaasa. Among these Prabhaasa is the chief. Prabhaasa was very close to his wife and would get her anything and everything that she aspires for.
Irrespective of births on different planets, Maya or Illusion played it's part in the form of 'Nandini', the sacred cow, which was in Vashista's [Vashista - a pious sage] ashram [meaning cottage or hermitage]. This 'Nandini' is the calf of 'Kamadhenu'. Similar to Kamadhenu, Nandini too has the powers to grant everything to its owner.
Prabhaasa's wife wanted to have Nandini and pleaded her husband to get her from the hermitage of Sage Vashista. Prabhaasa got carried away without thinking the consequences of what she was asking for. He thought of a plan to abduct Nandini. To execute his plan, he requested the help of other 7 vasus. While all together were trying to execute the plan, they were caught by the Sage Vashista by his mystic powers. As a result, Vashista cursed them to take birth as humans.
Repenting for the mis-deeds, all other 7 vasus requested the sage to show mercy on them. Vashista said, they would be freed from the curse once they're born excepting Prabhaasa, who would live for a long period on earth.