Kansa had imprisoned Devaki and Vasudeva. Devaki prayed to Vishnu. He promised to be born as her child. Accordingly, Devaki gave birth to her eighth child, incarnation of Lord Vishnu, on a stormy night on the eighth day of the month of Shravana.
Miraculously, the iron chains round Vasudeva opened. The guards fell asleep and a voice said, "Take your child to the safe arms of Nanda in Gokul."
Vasudeva placed the baby in a casket and stealthily crept out of the prison. Amidst heavy rains, Vasudeva crossed the river Yamuna carrying the new born on his head.
Seshnaga, the king of snakes, placed himself behind Vasudeva and spread his hood covering them like an umbrella. Vasudeva crossed the river safely and reached the gates of Gokul.