Amalaki Ekadasi (आमलकी एकादशी)
Lord Vishnu, major god of Hinduism and Indian mythology, popularly regarded as the preserver of the universe. Vishnu is the principle that sustains and preserves. Among the forces of nature, it is equilibrium. Whereas Brahma is called the "creator," it is Vishnu who "sustains the planets in their orbits" and rules the natural progression of the seasons and the ages. 
Vasishtha Muni said in Brahmanda Puran "Listen as I describe the best of all fast days, Amalakii Ekadashi. He who faithfully observes a fast on this Ekadashi obtains enormous wealth, gets free of the effects of all kinds of sins, and attains liberation. Fasting on this Ekadashi is more purifying than donating one thousand cows in charity to a pure brahmana."
Once, in the month of Phalguna (February - March), the holy fast of Amalakii Ekadashi arrived, conjoined with Dvadasi. This particular fast would bestow especially great benefit. Amalakii is offspring of Lord BrahmA, who can destroy all kinds of sinful reactions. Amalakii, is actually the form of Brahman, and was once worshiped by Lord Ramachandra Himself. Whoever circumambulates her is therefore immediately freed of all his sins.
After having bath offered Amalakii tree a pot filled with water, as well as garland and aromatic incense. Then worship Lord Parashurama with these prayers: 'Oh Lord ParashurAma, Oh son of Renuka, Oh all-pleasing one, Oh liberator of the worlds, kindly come beneath this holy Amalakii tree and accept our humble obeisances.'
If the Amarlaki tree isn't available then worship the sacred Tulasi tree. Also plant the sacred Tulasi seeds, and offer lamps to her.
The venerable Vasishtha Muni said, "...anyone who observes this holy Amalakii Ekadashi will undoubtedly attain the supreme abode of Lord Vishnu, so great is the religious merit earned from the observance of this most sacred fast day." 
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