It is three days after the Day of Sacrifice, and it is called that because the meat of the sacrifices is dried in the sun during these days. Fasting on these days is strongly disliked, as stated by the Prophet Muhammad (peace be upon him): "The days of Tashreeq are days of eating and drinking," in Sahih Muslim 2: 800, and in the selected hadiths 9: 254. Aisha and Ibn Umar (may Allah be pleased with them) said: "There is no permission to fast on the days of Tashreeq except for someone who cannot find a sacrifice," in Sahih Bukhari 2: 703. However, if a person begins to fast on the days of Tashreeq and breaks their fast, they are not required to make it up. But if someone vows to fast these days, it is valid, and if they break the fast, they must make it up. If they fast for the sake of a vow, they fulfill the vow despite the prohibition, as mentioned in Al-Hadiyah Al-Ala'iyah, p. 174.