This is a quotation from Srimad-Bhagavatam (10.34.9). The inhabitants of Vrndavana, under the leadership of Nanda Maharaja, once wanted to go to the bank of the Sarasvati on a pilgrimage. Nanda Maharaja was fasting, and he lay down near the forest. At that time a serpent, who was formerly cursed by Angirasa Rsi, appeared. This serpent had formerly been named Sudarsana, and he had belonged to the Gandharvaloka planet. However, because he joked with the rsi, he was condemned to take on the body of a big snake. When this serpent attacked Nanda Maharaja, Nanda Maharaja began to call, "Krsna! Help!" Krsna immediately appeared and began to kick the serpent with His lotus feet. Due to being touched by the Lord's lotus feet, the serpent was immediately freed from the reactions of his sinful life. Being freed, he again assumed his original form of Sudarsana, the Gandharva.