Q; Can you please provide me some information on The fast of 'Arafat Day'?
A; All-Praise is due to Allah,
It was reported from Abu Hurayrah (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “The promised day is the Day of Resurrection, the witnessed day is the Day of ‘Arafaah, and the witnessing day is Friday.” Narrated by al-Tirmidhi and classed as saheeh by al-Albaani.
It is the “odd” [i.e., odd-numbered, Witr] by which Allaah swore in the aayah (interpretation of the meaning):
“And by the even and the odd” [al-Fajr 89:3]. Ibn ‘Abbaas said: “The even is the Day of al-Adhaa [i.e., 10th Dhoo’l-Hijjah] and the odd is the Day of ‘Arafaah [i.e., 9th Dhoo’l-Hijjah] This is also the view of ‘Ikrimah and al-Dahhaak.
It was reported from Abu Qutaadah (may Allaah be pleased with him) that the Messenger of Allaah (peace and blessings of Allaah be upon him) was asked about fasting on the Day of ‘Arafaah. He said, “It expiates for the sins of the previous year and of the coming year.” Narrated by Muslim.
And Allah knows best...