After five hundred years, Kadru had one thousand sons. Vinata\’s eggs were not mature as yet, but she became so much impatient that she broke open one of her eggs and a half-developed child, Aruna, came out. After another five hundred years, the other egg of Vinata, which became fully developed, hatched itself and her second son Garuda was bom. On his pre-mature birth, Aruna cursed his mother to live as slave of Kadru till the birth of her second son.
After pronouncing the curse, Aruna rose to the sky and on the advice of Brahma, became the charioteer of sun-god, so that by standing before the god, the intensity of his heat may be reduced. It is said that Aruna broke the legs of some birds in one of his previous births, therefore in pursuance of the law of Kanna, he became a cripple as the brotner of Garuda. One cannot escape the punishment of previous actions.
References :
1. Kohli, Surindar Singh, Dictionary of Mythological References in Guru Granth Sahib, 1993