Feast of Ezid
Feast of Ezid (Kurdish: Cejna Êzî/Êzîd or Eyda Êzî/Êzid) is a Yezidi festival that commemorates Sultan Ezid.

Rojiyên Êzî
The Feast of Ezid is preceded by Rojiyên Êzî (The fasts of Ezid), which are the three days of fasting in honor of Êzî/Ezid one of the names of God and also considered to be the name of God's earthly manifestation in Yezidism. Êzî is one of the names of God and at the same time namesake of the Yezidis (Êzidî). The name Êzidî therefore means “Follower of God”. Unlike the fasting days of Rojiyên Sêşims and Rojiyên Xwudan during the preceding weeks, the three fasting days of Rojiyên Êzid are compulsory for every Yezidi with exception of children, the sick and elderly. The fastings begin on Tuesday and end on Thursday, starting after sunrise and ending after sunset each day.

Winter solstice
This festival takes place on the Friday before winter solstice, it marks a turning point in the solar cycle. As the days get longer after the winter solstice, believers believe that the Sun is being reborn. The winter solstice is also associated with the appearance of divine figures. The Yazidis associate winter solstice with the appearance of Siltan Ezid, an important religious figure who is considered as God's earthly manifestation.

References

Sources 
Yezidis Russia
December observances
Yazidi holy days
Yazidi religion
Winter solstice