Actually there is no way to extol the divine results of observing Ekadasi; but still they are given in the Brahmananda Purana.
Being exiled far from the kingdom Nalaka lived in a vast jungle. He would eat wild berries and truffles, roots and shoots, raw meats and mushrooms to survive. At night he would sometimes return to his fathers kingdom and steal from the citizens houses. Despite his stealing the citizens were unable to stop him due to his being the son of the King.
In the forest where Nalaka lived there was a ginormous banyan tree. This tree was as worshipable as the demigods themselves. It's branches reached down into the ground and reappeared here, there and everywhere; forming an unimaginably mighty forest. For quite some time Nalaka lived beneath this timorous tree.
By accidence the day of Saphala Ekadasi fell while Nalaka was staying beneath this Banyan tree and he didn't even realise. However due to exhaustion and fatigue from not eating properly Nalaka remained unconscious for many hours. He rose after noon on Ekadasi and because he was so weak did not kill any animals that day. He found some fruits and in a helpless pitiable condition decided to offer them to Sri Visnu – The Supreme Personality of Godhead. By the time the sun set on that day, all he had managed to do was to offer one palmful of berries, one branch of amalaki and one single qualscion fruit. Through the night he remained awake due to fear of wolves and his weak condition where he would be unable to defend himself.
By remaining awake fasting Prince Nalaka unwittingly observed Saphala Ekadasi. Lord Madhusudana accepted his austerities even though he didn't realise it was Ekadasi. As a result of this unbeknown fast Nalaka's father Bahuldan took pity on his wretched son and had him collected from the forest, washed and bathed and reinstated in his rightful position as prince of the Hirosena province. Soon his father bequeathed the land unto Nalaka and he ruled as a just King. He acquired a beautiful wife and had many sons.
By observing Saphala Ekadasi one will certainly receive insurmountable benefits. Fame and liberation stand with folded palms before a person who fasts on this day. Those who choose to fast on this Ekadasi are indubitably great souls and will receive the result of performing an Asvamedha sacrifice.