“Fasting on the Day of Arafah absolves the sins of two years: the previous year and the coming year, and fasting on Ashura, (the tenth day of Muharram) atones for the sins of previous years.” Reported by all except Al-Bukhari and At-Tirmidhi
“Four things the Messenger of Allâh never neglected: Observing fast on the day of Ashura, Arafat, three days every month, and offering Fajr Sunnah prayers early in the morning.” Muslim
These statements are proof that fasting on the 9th of Dhul-Hijjah, the day before ‘Eid UL Adha was a lifelong practice of the Prophet, peace be upon him, as his wife reported.
There are some reports that fasting is prohibited on the Day of Arafah. However, it must be understood that this refers to a person performing the Hajj. If a person is on the Hajj, there is no fast for him or her on the day of Arafah. That is undoubtedly a blessing for him because of the hardships of the pilgrimage. In a saying reported by Umm Al-Fadl, may Allah be pleased with her, she said:
“The companions doubted whether the Prophet was fasting on Arafah or not. She decided to prove to them that he was not, so she said, ‘I sent to him milk, which he drank while he was delivering the Khutbah (sermon) on Arafah. “Recorded by Al-Bukhari
Prohibiting the pilgrims from fasting on these days is a great mercy for them, for fasting will exert undue hardship on the person performing the Hajj, while they are primarily concerned with their pilgrimage. Above all, the Pilgrims would not be fasting anyway because he is travelling.