Shayani Ekadashi

Shayani Ekadashi is on Tuesday, July 20. 

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According to Wikipedia:
Shayani Ekadashi is also called (lit. "sleeping eleventh") or Maha-ekadashi (lit. "The great eleventh") or Prathama-ekadashi (lit. "The first eleventh") or Padma Ekadashi or Devshayani Ekadashi or Devpodhi Ekadashi is the eleventh lunar day of the bright fortnight of the Hindu month of Ashadha (June - July). Thus it is also known as Ashadhi Ekadashi or Ashadhi.It is known as Toli Ekadashi in Telugu.This holy day is of special significance to Vaishnavas, followers of the Hindu protector God, Lord Vishnu. 

Ekadashi Tithi will begin at 09:59 pm in July and will prevail till 07:17 PM on July 20. Those observing Ekadashi fast can do Parana on Dwadashi tithi, that is, July 21 between 05:36 am to 08:21 am.

As per Hindu belief, Lord Vishnu falls asleep in Ksheersagar – cosmic ocean of milk – on Shesha nāga, the cosmic serpent on Shayani Ekadashi. Vishnu finally awakens from his slumber four months later on Prabodhini Ekadashi. This period is known as Chaturmas (lit. “four months”) and coincides with the rainy season. Thus, Shayani Ekadashi is the beginning of Chaturmas. Devotees start observing the Chaturmas vrata (vow) to please Vishnu on this day.

On Shayani Ekadashi, devotees observe a fast and avoid consuming grains, beans, cereals, certain vegetables like onions, and some spices. Lord Vishnu’s idol is adorned in bright yellow clothing and worshipped by offering flowers, betel, betel nut, and bhog. The puja is concluded by taking prasad. Devotees also stay awake all night on Ashadhi Ekadashi and sing bhajans.

This day, a huge religious procession of pilgrims known as Pandharpur Ashadi Ekadasi Waari Yatra culminates at Pandharpur, in Solapur district in south Maharashtra, situated on the banks of the Chandrabhaga River. Pandharpur is main center of worship of the deity Vitthal, a local form of Vishnu. Lakhs (hundreds of thousands) of pilgrims come to Pandharpur on this day from different parts of Maharashtra. Some of them carry Palkhis (palanquins) with the images of the saints of Maharashtra. Dnyaneshwar's image is carried from Alandi,Namdev's image from Narsi Namdev, Tukaram's from Dehu, Eknath's from Paithan, Nivruttinath's from Trimbakeshwar, Muktabai's from Muktainagar, Sopan's from Sasvad and Saint Gajanan Maharaj from Shegaon. These pilgrims are referred to as Warkaris. They sing Abhangas (chanting hymns) of Saint Tukaram and Saint Dnyaneshwar, dedicated to VitthalBig text.

Read more on: 
https://www.news18.com/news/india/shayani-ekadashi-significance-puja-vidhi-and-shubh-muhurat-3976748.html 
https://www.moneycontrol.com/news/india/devshayani-ekadashi-2020-heres-all-you-need-to-know-5485881.html