Musnad Ishaq

Benefits:
It is narrated in Sahih Bukhari from Sayyidah Umm Fadl bint Harith radi Allahu anha that on the day of Arafah, some people differed regarding the fasting of the Messenger of Allah sallallahu alayhi wa sallam. Some said: He sallallahu alayhi wa sallam is fasting, and others said: He is not fasting. Upon this, Sayyidah Umm Fadl radi Allahu anha sent a bowl of milk to him sallallahu alayhi wa sallam (so that the reality would become clear). He sallallahu alayhi wa sallam was mounted on his camel, and he drank the milk. (Bukhari, no. 1988)

Sayyiduna Abu Hurairah radi Allahu anhu states that the Messenger of Allah sallallahu alayhi wa sallam forbade fasting in Arafat, saying: "Do not fast in Arafat." (Sunan Abi Dawud, Book of Fasting, no. 2440)

This prohibition is for the pilgrims (hujjaj), whereas for non-pilgrims this fast is legislated (mashru‘). Because this fast has great virtue: through it, the minor sins of two years are forgiven. As the Messenger of Allah sallallahu alayhi wa sallam said: ((Fasting on the day of Arafah, I hope from Allah that it will expiate the sins of the previous year and the coming year.)) (Sunan Ibn Majah, no. 1730) ... "I have hope in Allah that for the fast of the day of Arafah, Allah will forgive the fasting person's sins of the previous year and the coming year."