Nirjala Ekadashi – Wikipedia

Nirjala Ekadashi is a Hindu holy day falling on the 11th lunar day of the waxing fortnight of the Hindu month of Jyestha (May/June). This ekadashi derives its name from the water-less (Nir-jala) fast observed on this day. It is considered to be the most austere and hence the most sacred of all 24 Ekadashis.

: https://en.wikipedia.org/wiki/Nirjala_Ekadashi