(227) Chapter: The Excellence of Observing Saum on the Day of 'Arafah, 'Ashura' and Tasu'a (i.e., 9th of Muharram)

Abu Qatadah (May Allah be pleased with him) reported:
The Messenger of Allah (ﷺ) was asked about the observance of Saum (fasting) on the day of 'Arafah. He said, "It is an expiation for the sins of the preceding year and the current year."

[Muslim].

Commentary: The ninth day of Dhul-Hijjah is called Yaum-`Arafah . On this day, pilgrims stop and stand in prayers at `Arafat which is the most important ritual of Hajj, so much so that Hajj is deemed incomplete without it. On that day, the pilgrims are engaged in the remembrance of Allah and prayers as that is their most important worship on that day. For this reason, Saum is not desirable for them, but for other people, Saum has a special merit. The importance and merit of this Saum can be judged from the fact that it expiates sins for two consecutive years: the previous year and the current year. But these sins relate only to the minor sins, not the major ones, or become a means of elevation of one's status.