King Ambarisha was a great devotee of Lord Hari (Vishnu). He observed the Ekadashi Vrata (vow) diligently for one year and obtained His Grace. On one occasion Ambarisha fasted for three consecutive days. As he was about to break his fast the prescribed time, Rishi Durvasa appeared as his guest. The king received him with due respect and offered him food.The Rishi wanted to take a bath first and went to the river. The king waited patiently for a long time, but the sage did not return. Time was running out; if the king did not eat anything before the auspicious time ended, his Vrata would not bear fruit. But if he ate, he would be showing disregard to the Rishi, his respected guest. As a compromise the king, on the suggestion of his advisors, took a little water to serve both the conditions.
When Durvasa returned, he knew exactly what had happened and became angry. He tore a hair from his tuft and turned it into a demon, whom he ordered to kill Ambarisha. The king was unmoved. He was protected by the Sudarshana Chakra, the weapon of Lord Vishnu, which destroyed the demon. The powerful chakra then began to chase Durvasa; it followed the Rishi wherever he went and tried to destroy him.
In fear, Rishi Durvasa went to first to Brahma and then to Siva for help, but to no avail. He went to Lord Hari who said to him, “I am dependent on My devotees. My heart is in the possession of My devotees. It is best if you go to Ambarisha and beg his pardon. This is all that can save you.”Ambarisha thereupon prayed to Sudarshana Chakra (the Lord’s weapon) to desist from its course, and saved the Rishi. Durvasa thanked him from the bottom of his heart. This story demonstrates the great spiritual power generated by the observance of Ekadashi.