Significance and legend
Krishna tells Yudhishthira the story of King Harishchandra of the solar dynasty, renowned for never speaking an untruth. To fulfil a promise made to the sage Vishvamitra, Harishchandra gave away his entire kingdom, and to pay the remaining dakshina he sold his wife and son and then himself into servitude. He came to work for a chandala at the cremation ground in Kashi, collecting fees from those who brought their dead, all the while holding firmly to truth.
One day, as he sat in sorrow, the sage Gautama came to him. Hearing his story, the sage told him that the Ekadashi of the dark fortnight, called Aja, was approaching, and advised him to observe it with full devotion. Harishchandra kept the fast and vigil, and by its power his past karma was exhausted. The gods appeared, his dead son was restored to life, he was reunited with his wife, and he regained his kingdom. The story shows that even the greatest suffering can be overcome by truthfulness combined with devotion.
How Aja Ekadashi is observed
Devotees take a single meal on Dashami and fast on Ekadashi, worshipping Vishnu as Upendra with tulsi, sandal, flowers and lamps. The story of Harishchandra is read, and the day is spent in prayer and truthful speech. Charity of food, which gives the day its other name Annada, is especially recommended. Night vigil is kept, and the fast is broken on Dwadashi after sunrise within the parana window, after offering food to Vishnu and the needy.