The Official Website of Grand Ayatollah Makarem Shirazi

Fasting is disliked on several occasions which are as follows 1. Fasting on the day of Ashura 2. Fasting on the day that one doubts whether it is the day of Arafah or Eid al-Aḍḥā 3. The fast of guests without the consent of their host But fasting on any day of the year except for Haram and Makrūh fasts is recommended However, it has been recommended more to fast on some days which are as follows 1. The first and last Thursday of a lunar month and the first Wednesday after the 10th day of each lunar month If one does not fast on these days it is recommended that they make up for the missed fasts 2. The 13th, 14th and 15th of each lunar month 3. The entire month of Rajab and Shaban However, in the event that one is not able to fast for the whole month, they can fast as much as they can 4. The fast of the 24th of Dhu al-Ḥijjah and the 25th of Dhu al-Qadah 5. Fasting from the 1st to the 9th of Dhu al-Ḥijjah on the condition that on the 9th day of Dhul-Hajjah which is the day of Arafah, physical weakness from fasting does not cause one to miss out on Arafah dua in which case fasting on the 9th day of Dhul-Hajjah is disliked 6. Fasting on the auspicious day of Eid al-Qadir 7. Fasting on the 1st, 3rd and 7th day of Muharram 8. Fasting on the birthday of the most noble Prophet of Islam (s), which is the 17th of Rabī‘al-Awwal 9. Fasting on the day of the Mab‘ath of the Holy Prophet of Islam(s), 10. Fasting on Nowruz. If one observes a recommended fast, it is not obligatory upon them to continue fasting until the end of the day and they can break the fast whenever they wish. Even if a fellow believer invites one observing a recommended fast to eat, it is advisable that they accept the invitation and break their fast, in which case they are also rewarded with a thawab of the fast but on the condition that the host is in earnest about the invitation.