Kadru and Vinata were the wives of Sage Kashyapa. The story of them are found in Mahabharata and the Puranas
Once Kadru and Vinata put a bet on the color of the tail of
the horse Uchaishravas – a seven-headed flying horse that was obtained during
the churning of ocean or Samudra Manthan.
Kadru claimed the color was black and Vinita claimed it was
white. The stake was whoever lost the bet will serve the other.
Kadru cheated by asking her sons, the Nagas, to hang on to
the tail of Uchaishravas. Thus the white tail of the divine horse turned black
as the nagas hung on to them.
Vinita and Garuda were thus forced to serve Kadru. They were
treated badly by Kadru and her sons.