Yogini Ekadasi occurs during the waning Moon in the month of Ashadha (June/July) and it's glories are described in the Brahma Vaivarta Purana. Once Maharaj Yudhisthira enquired from Sri Krsna, "O Supreme Lord! O Madhusudana! You have described the insurmountable glories of Nirjala Ekadasi. Now I very much wish to hear about the Ekadasi that takes place during the waning Moon in the Ashadha month.