Which days is it forbidden to fast?

In our religion, just as there are days when fasting is commanded or recommended, there are also days when fasting is forbidden or discouraged. Depending on the nature and severity of the prohibition, fasting on some of these days is considered haram or severely disliked (tahrîmen makruh), while on others it is mildly disliked (tenzîhen makruh).

The foremost among the days on which fasting is forbidden are the festival (Eid) days. The Prophet (peace be upon him) stated that fasting is not to be observed on two occasions: the first day of Eid al-Fitr and the days of Eid al-Adha. (Bukhari, Sawm, 66-67 [1990-1991, 1993]; Muslim, Siyam, 138-139 [1137-1138]) It is forbidden to fast only on the first day of Eid al-Fitr and on all four days of Eid al-Adha. (Mawsili, al-Ikhtiyar, 1/125-126) The reason for this prohibition is that these are days of eating, drinking, and joy. Eid al-Fitr is considered a “general iftar feast” after a month of fasting for the sake of Allah (the Almighty). For this reason, it is called the “festival of breaking the fast (fitr/iftar).” The first day of Eid al-Fitr thus serves as the iftar for the month of Ramadan. To fast on such a communal day of breaking the fast would mean not participating in Allah’s (the Almighty) feast, which is at the very least considered improper. The days of Eid al-Adha, when sacrifices are offered for Allah, are also days of feasting. The Prophet (peace be upon him) stated that the days of tashriq are days of eating, drinking, and remembering Allah. (Muslim, Siyam, 144 [1141])

For pilgrims, if there is a risk of weakness and exhaustion, it is preferable not to fast on the 8th (“Tarwiyah”) and 9th (“Arafah”) days of Dhu al-Hijjah. The Prophet (peace be upon him) forbade those present at Arafat on the day of Arafah from fasting. (Abu Dawud, Sawm, 63 [2440]; Ibn Majah, Siyam, 40 [1732]) This is because it is better for them to be energetic and lively while performing the pilgrimage than to have observed a voluntary fast beforehand.

Fasting on certain other days is considered disliked (makruh) for various reasons. For example, fasting only on the day of Ashura (the 10th of Muharram) is considered makruh because it resembles and imitates the practice of the Jews. (Muslim, Siyam, 133 [1134])

It is also makruh to fast on the “day of doubt” (yawm al-shakk)—the day at the end of Sha’ban when it is uncertain whether it belongs to Sha’ban or Ramadan. The Prophet (peace be upon him) forbade welcoming Ramadan by fasting a day or two in advance. (Bukhari, Sawm, 14 [1914]; Muslim, Siyam, 21 [1082])

It is also makruh to fast for two or more consecutive days without breaking the fast in between. This is called the fast of wisal (sawm al-wisal). According to Aisha (may Allah be pleased with her), the Prophet (peace be upon him) forbade fasting in this manner; when reminded that he himself did so, he replied, “I am not like you; my Lord feeds me and gives me drink.” (Muslim, Siyam, 61 [1105])

Source: T.C. Diyanet İşleri Başkanlığı, Din İşleri Yüksek Kurulu