A hadith narrated by one of the wives of the Prophet, peace and blessings be upon him, states:

Reported by Abu Dawud (2437) and graded authentic by al-Albani. Some scholars have discussed the chains of the hadith about fasting the nine days because its narrations differ. These reports do not therefore establish with certainty that the Prophet, peace and blessings be upon him, fasted all nine days every year. Nor does the recommendation to fast them depend solely on these reports: fasting is included among the righteous deeds generally encouraged during these days.

It is also reported that Aishah, may Allah be pleased with her, said:

Reported by Muslim (1176). Among the ways al-Nawawi mentioned for reconciling the reports are that the Prophet may have refrained from fasting because of a circumstance, or that she did not see him fasting during them. These are explanations proposed by scholars, not an established report about why he did not fast. Her hadith does not indicate that fasting is prohibited; its recommendation is established by the evidence concerning the virtue of righteous deeds.

Ibn Rajab, may Allah have mercy on him, mentioned in Lataif al-Maarif that Abdullah ibn Umar, may Allah be pleased with him and his father, used to fast these days. He also reported statements from al-Hasan, Ibn Sirin, and Qatadah concerning the virtue of fasting them, and that this was the view of most scholars or many of them.

Ibn Rajab also reported that Ibn Sirin disliked the expression "he fasted the ten days," lest it be understood to include the Day of Sacrifice. Thus, the common expression "fasting the ten days" here refers to the nine days before Eid.

For the pilgrim standing at Arafah, the Sunnah is not to fast, following the Prophet, peace and blessings be upon him. This is not limited to those who would find fasting difficult. Umm al-Fadl, may Allah be pleased with her, sent him a cup of milk while he was at Arafah, and he drank it; reported by al-Bukhari (1988). Not fasting also helps the pilgrim with supplication, remembrance, and the rites of Hajj.

For someone not performing Hajj, the Sunnah is to fast the Day of Arafah if able.

Fasting these days is voluntary. It does not become obligatory simply because Dhul-Hijjah begins, unless a person is required to fast for another reason, such as a valid vow. Neither consecutive fasting nor fasting the preceding days is a condition for a valid fast on Arafah. Fast what you can, without undertaking fasting that harms you or causes you to neglect an obligation.

Anyone unable to fast may remember Allah, supplicate, give charity, and pursue other opportunities for good. No fidyah is required for leaving this voluntary fast. Other deeds are discussed in The Best Deeds in the First Ten Days of Dhul-Hijjah.

It is permissible to fast Arafah on its own when the intention is to observe Arafah, not to single out Friday for its own sake. Shaykh Ibn Baz permitted this and mentioned that fasting Thursday with it is more complete. If one is able to do so, that is good, but fasting the preceding day is not a condition for a valid Arafah fast. The day after Arafah is Eid, and fasting it is not permissible.

Begin by maintaining your prayers and fulfilling the rights of those around you. Guard your tongue against backbiting and lying. Recite the Quran, supplicate, and give charity as you are able, honor your parents, and maintain family ties. Do not burden yourself with an exhausting schedule or a different supplication for every hour. Supplicate using what is found in the Quran and Sunnah and ask for the permissible good you need.

Among the deeds of these days are takbir, tahlil, and tahmid: declaring Allah's greatness, affirming that none has the right to be worshipped except Him, and praising Him. These are observed before, during, and after Arafah, and remembrance is not limited to those fasting. For the times and wording, read Takbir in the First Ten Days of Dhul-Hijjah.