The three days following Eid al-Adha are the Days of Tashriq (the 11th, 12th and 13th of Dhu’l-Hijjah). These days are mentioned by Allah when He says: Remember Allah during the Appointed Days (2:203). The Messenger of Allah ﷺ described them as days of eating and drinking and remembrance of Allah (Muslim, Ahmad and al-Nasa’i). Fasting is thus forbidden on Eid and the Days of Tashriq. Just as we tried to draw close to Allah by fasting before Eid, we now draw close to Him by enjoying that which He has bestowed us with. All that the slave must do is obey the order of his Lord, knowing that therein is His pleasure and safety from following his own caprice.
Anyone who wishes to fast the White Days must not fast on the 13th of Dhu’l-Ḥijjah. They can fast the 14th, 15th and 16th instead.