It is recommended for those who are not performing Hajj to fast on the Day of Arafah - which is the ninth day of Dhul-Hijjah - because it has a virtue over other days, as mentioned in Bada'i' al-Sana'i' 2: 79; from Abu Qatada (may Allah be pleased with him), the Prophet (peace be upon him) said: "Fasting on the Day of Arafah, I hope from Allah that it expiates the sins of the year before it and the year after it," in Sahih Muslim 2: 818, and Sahih Ibn Hibban 8: 394. As for the pilgrim, if fasting weakens him from standing and supplicating, it is disliked as a matter of etiquette; because the virtue of fasting on this day can usually be made up in other years, while the virtue of standing and supplicating on this day cannot usually be made up for the general public except once in a lifetime, so it is more appropriate to secure it. The dislike here is for etiquette; because it is a neglect of the more important matter at that time, unless it causes him to behave poorly and fall into what is prohibited; from Umm al-Fadl bint al-Harith (may Allah be pleased with her): "Some people argued with her on the Day of Arafah about the fasting of the Messenger of Allah (peace be upon him), some said: He is fasting, and some said: He is not fasting, so she sent him a cup of milk while he was standing on his camel at Arafah and he drank it," in Sahih Muslim 2: 791, and Sahih al-Bukhari 2: 598, and from Ibn Umar (may Allah be pleased with them): "He performed Hajj with the Prophet (peace be upon him), then with Abu Bakr, then with Umar, then with Uthman, and none of them fasted it." However, if fasting does not weaken him from standing and supplicating, it is not disliked; due to the combination of two acts of worship. See: Bada'i' al-Sana'i' 2: 79, Fath al-Qadir 2: 478, al-Bahr al-Ra'iq 2: 365, Hashiyat al-Tahbih 1: 332, and Majma' al-Anhar 1: 254.