It is disliked if it weakens him from standing and supplicating; because the virtue of fasting on this day can be compensated for in other years and is usually compensated for. However, the virtue of standing and supplicating on this day cannot be compensated for by the general public except once in a lifetime, so it is preferable to secure it. The dislike here is a matter of recommendation; because it is a neglect of what is more important at that time, unless he behaves poorly and falls into a prohibition. It was narrated by Umm al-Fadl bint al-Harith, may Allah be pleased with her: "Some people disputed 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." This is 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 Abu Bakr, then Umar, then Uthman, and none of them fasted it." However, if it does not weaken him from standing and supplicating, it is not disliked; because it combines both acts of worship. Refer to: 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.