Shaykh Maulana Abdul Aziz Alvi
Hadith Commentary: Benefits and Issues: The days of Tashreeq refer to the four days from the 10th of Dhul-Hijjah to the 13th of Dhul-Hijjah. Since these are days of eating and drinking, it is not permissible to fast during them. However, in the Noble Qur’an, regarding the mutamatti‘ (one performing tamattu‘ Hajj), it is stated that if he does not have a sacrificial animal (hady), then he should fast ten days, and:
(ثَلاثَةِ أَيَّامٍ فِي الْحَجِّ)
—that is, three days must be fasted during the days of Hajj. And this verse is general, whether these days are before the sacrifice or after it. Therefore, there is a difference of opinion among the imams on this issue.
According to the preferred opinion of Imam Abu Hanifah rahimahullah and Imam Shafi‘i rahimahullah, fasting during the days of Tashreeq is not permissible for anyone. However, according to Imam Malik rahimahullah, Imam Ahmad rahimahullah, Imam Ishaq rahimahullah, and one opinion of Imam Shafi‘i rahimahullah, fasting during the days of Tashreeq is permissible for the mutamatti‘, qarin, and muhsar.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 2677