Indira Ekadashi is said to be of great significance for salvation of ancestors. Ancestors up to 7th generation of the person performing this fast attain salvation along with that person. On this day Lord Shaligram is worshipped.
This Ekadashi comes in Shraddha Paksha and with its result the ancestors get salvation.
The pooja Vidhi of this Ekadashi is as follows:
During Satyuga, a king named Indersena ruled the city of Mahishmati. His parents had died. One night he dreamed that his parents were experiencing highly pain and sufferings in hell. The King got worried by the plight of his ancestors. He thought of ways to free them from the pain of hell. He discussed the dream with his advisers and Brahmin scholars who said - : O Rajan! If you do the fast of Indira Ekadashi along with your wife, then your ancestors will attain salvation. On this day, worship Lord Shaligram with Basil leaves, etc and offer food and donation to Brahmins needy people. With their blessings, your parents and forefathers will go to heaven.”
Following their advice, the King along with his wife performs the fast of Indira Ekadashi ritually. At night when he was sleeping, God appear and said to him - “Rajan! Your ancestors have attained salvation from the influence of your fast.” Since then only, the significance of Indira Ekadashi Vrat increased.