In the Puranas, Vishnu goes to rest on the serpent Shesha in the ocean of milk on Devshayani Ekadashi in the month of Ashadha and awakens four months later on Prabodhini Ekadashi. This four-month period is called Chaturmas (the four months), a time traditionally given to prayer, fasting, study and simple living, when many families postpone weddings, house-warmings and other new beginnings. Dev Uthani Ekadashi marks the close of this period, and the name Prabodhini itself means 'the one who awakens'.
Because the preserver of the world is believed to be awake again, the day is seen as the reopening of the season for auspicious work. Across North and West India the wedding season traditionally begins from this point, and families who have been waiting through Chaturmas start fixing dates for marriages, engagements and other ceremonies with the help of a priest.
Like every Ekadashi, it is a day for fasting and devotion to Vishnu, and it is counted among the most important Ekadashis of the year along with Devshayani (Ashadhi) Ekadashi. It also opens Bhishma Panchaka, the last five days of Kartika ending on Kartika Purnima, which many devotees keep with extra discipline, and in many regions it begins the season of Tulsi Vivah.
The best-known account links the four months of rest to the story of Vamana, Vishnu's dwarf incarnation. Vamana asked the generous demon king Bali for three steps of land and then covered the earth and the heavens in two strides; Bali offered his own head for the third. Pleased with his humility and devotion, Vishnu sent Bali to rule the netherworld (Patala) and, in the traditional telling, promised to stay with him there for part of each year. These are the months of Chaturmas, and on Prabodhini Ekadashi Vishnu returns and resumes his care of the world.
Another tradition in the Puranas tells that after long and tiring battles with demons, Vishnu lay down to rest on Shesha in the ocean of milk, and the gods and sages waited for him to wake. On Kartika Shukla Ekadashi they gathered with songs, conch shells and prayers to awaken him. Families re-enact this moment each year when they sing, ring bells and recite the awakening verse in the evening puja.