Ekadashi in Krishna Paksha during Paush month is known as Saphala Ekadashi. As Saphala means achievement, so it is assumed that by fasting on this day all tasks of a person get prosperous. On this day, Lord Achyuta is worshipped.
Peoples fasting for Saphala Ekadashi must worship Lord Achyuta on this day. The pooja Vidhi for the fast is as follows:
In religious scriptures, significance of Saphala Ekadashi is mentioned during the conversation between Lord Krishna and Dharma raj Yudhishtara. It is believed that 1000 Ashwamedha Yagya cannot give as much result as one can obtain by fasting for this Ekadashi. So, if a person fasts on this day, all his/her pain and suffering ends, luck becomes favorable and wishes get fulfilled.
In ancient times, King Mahishmat used to rule the Champawati city. He had four sons, among which Lumbhak’s was very Brutal and immoral. He used to spend his father’s money on bad works. Getting frigid by his wrong doings, the King deported him; still Lumbhak’s habits of loot and larceny did not end. One time, he did not get food for 3 days. Wandering around, he reached the hut of a saint. Fortunately, it was Saphala Ekadashi on that day. So, the hermit welcomed him and presented him food. Witnessing this behavior of the sage changed Lumbhak’s. He fell to the saint's feet and asked for his blessings. The saint made him his disciple and with time, Lumbhak’s character became well good and clean. As per his guidance, Lumbhak’s started fasting for the Ekadashi. When he changed completely and became a good man, the hermit showed his true form to him. It was his father in the form of the hermit. After this, Lumbhak’s handled his amenability greatly as King and set an example in front of every person. And he kept on fasting for Saphala Ekadashi till he lived.