Significance and legend
Padmini Ekadashi, also called Kamala Ekadashi or Purushottami Ekadashi, falls in the bright fortnight of the adhika masa, the intercalary month that is added roughly every three years and is dedicated to Vishnu as Purushottama. In the Padma Purana, Krishna tells Yudhishthira of King Kritavirya of Mahishmati, who had many queens but no son. He went to the forest with his queen Padmini, said to be the daughter of King Harishchandra, and performed severe austerities for years, but no son was born.
Padmini then sought the counsel of Anasuya, the devoted wife of the sage Atri. Anasuya told her of the special Ekadashi of the bright half of the adhika month and its method of observance. Padmini kept the fast with complete devotion, and Vishnu appeared and granted her a boon. She asked for a son who would be unconquerable, and in due course she gave birth to Kartavirya Arjuna, the thousand-armed king, who became so powerful that he defeated even Ravana.
How Padmini Ekadashi is observed
Because it occurs only in an adhika month, this Ekadashi is regarded as rare and especially meritorious. Devotees fast, worship Vishnu as Purushottama with lotus flowers, tulsi and lamps, and keep vigil through the night with chanting and scripture reading. Charity and service are emphasised throughout the adhika month. The fast is broken on Dwadashi after sunrise within the parana window, after offering food to Vishnu and to Brahmins or the needy.