EKADASI, from Sanskrit ekadasa; eka(one)+ dasa (ten) meaning eleven, is the eleventh day of the lunar fortnight, in both its dark and light halves. Among Vaisnavite Hindus, ehkadasi also harivasar (lit. Visnu`s day) is a day of fasting. Partaking of food in any form on this day is considered a sin, while observing a fast on this day is believed to be meritorious. In the Sikh system no special sanctity attaches to any particular day, nor any demerit. As says Guru Amar Das, Nanak III: The fifteen lunar days, seven days of the week, Months and seasons repeat themselves endlessly; So do the days and nights.

That is how the world goes. Coming and going is by the Creator`s Will; The Creator alone is truth immutable. (GGS, 842) According to Guru Nanak, a true Ekadasi is observed by him who lodges the One in his heart and who eschews violence and worldly allurements. Engrossed in superstition, one does not perceive the essence .In the same tone is Guru Arjan`s verse in the Gaun measure: On Ekadasi see God by your side, Controlling your passion, listen to the Lord`s praise. Let contentment reside in your heart and compassion for all living beings; Thus will your brata be fulfilled. (GGS, 299)

References :

1. Sabadarth Shri Guru Grandh Sahib.Amritsar, 1964