Cold Food Festival

1. The Cold Food Festival or Hanshi Festival is a traditional Chinese holiday celebrated for three consecutive days starting the day before the Qingming Festival in the Chinese Calendar, which falls on April 5 by the Gregorian calendar, except in leap years (the 105th day after dongzhi) and it has been absorbed into the Tomb Sweeping Festival, which occurs on April 4 or 5th each year.
2. It is celebrated in China as well as the nearby nations of Korea and Vietnam. 
3. As the legend goes, during China’s Spring and Autumn Period following a civil war, Prince Chong Er was forced into exile for 19-years and with him was his loyal minister, Jie. 
4. When the pair had run out of food and were starving, Jie cut the flesh from his own leg and made a leg soup from it to feed the Prince, taking loyalty to a whole new level.
5. When the hard times were over and the Prince became King, he rewarded all those who had remained loyal to him and totally overlooked the guy who CUT THE FLESH OFF HIS OWN LEG TO FEED HIM. 
6. Jie packed up his bags and disappeared into the wilderness, taking  his mom with him and someone finally confronted the King about his major oversight and feeling ashamed, he went off in search of Jie, but never found him. 
7. In result, some idiot suggested setting the entire wilderness on fire to smoke him and his moms out so, that’s just what the king does and when the fire was extinguished poor, loyal Jie is found dead in the forest, underneath a willow tree, with his mother on his back. 
8. Inside the tree is a letter, written in blood from Jie, “Giving meat and heart to my lord, hoping my lord will always be upright. An invisible ghost under a willow tree is better than a loyal minister beside my lord.”
9. In honor of Jie’s death, the King decreed that no fires could be lit on this day and created the Hanshi Festival or “Cold Food Festival,” since food could not be cooked.
10. Thus, there exist a Chinese Proverb that goes "While one can burn off an entire mountain, others are refrained even to light up to eat their rice" - depicting what transpired in the burning of the mountain and the subsequent annual banning of using fire on that day to commemorate.
11. In Korea, it is called Hanshik. It is a traditional Korean holiday. In the modern version of Hansik, people welcome the warm weather thawing the frozen lands. On this day, rites to worship ancestors are observed early in the morning, and the family visits their ancestors' tombs to tidy up. 
12. In Vietnam, where it is called Tết Hàn Thực, the Cold Food Festival is celebrated by Vietnamese people in the northern part of the country on the third day of the third lunar month, but only marginally. People cook glutinous rice balls called bánh trôi on that day but the holiday's origins are largely forgotten, and the fire taboo is also largely ignored.

References:

https://en.wikipedia.org/wiki/April_5

https://nourishingdeath.wordpress.com/2014/04/05/cold-food-festival-and-qingming-festival-tomb-sweeping-day-2/

http://www.china.org.cn/culture/2008-04/07/content_14407806.htm

https://en.wikipedia.org/wiki/Cold_Food_Festival

https://www.youtube.com/watch?v=bOxWx9HlaaY