Assalamu Alaikum Brothers and Sisters in Islam,
The Messenger of Allah (sal Allahu alaihi wa sallam) was asked about fasting on the Day of Arafah. He said, "It expiates the sins of the previous year and of the coming year." [Sahih Muslim]
The Day of Arafah, ninth Dhul Hijja, is the day of forgiveness for the pilgrims, who are present this day at Arafa, as well as for those who fast the Day of Arafa the world over. This fasting is mustahab (recommended) for those who are not on Hajj. In the case of the one who is on Hajj, it is not Sunnah for him or her to fast on this day, because the Prophet (salallahu alaihi wa sallam) did not fast on this day when in Arafa. In fact, it is narrated that he forbade fasting on the Day of Arafa when in Arafa. The Hajis presence in Arafa is itself very pleasing to Allah (subhanahu wa ta'ala). Regarding them, Allah (subhanahu wa ta'ala) says to His angels, "Look at my slaves, how disheveled and dusty they came to me, I do call you as witnesses upon me that I forgive them (their bad deeds)." [Ahmad]
Not everyone can go on Hajj, and certainly not every year, but the Day of Arafah is one of the great gifts of Allah (subhanahu wa ta'ala) that people all over the world can benefit from. On this day, Allah (subhanahu wa ta'ala) grants fasting Muslims forgiveness for their faults of two years, if they have committed any, if not, Allah (subhanahu wa ta'ala) elevates their degree in Paradise. The Muslims should celebrate the day of Arafa by restraining themselves from committing sins and iniquities in order that Allah may forgive them.
The Prophet of Allah (sallalahu alaihi wa sallam) said: "On this day (of Arafa) whomsoever holds his hearing, sight, and tongue (from committing sins), he will be forgiven by Allah." [Ahmad] Muslims should say the Tahlil (La ilaha il Allah), Tasbeeh (Subhanallah) and Takbeer (Allahu Akbar). It is also recommended to do as much dua (supplication) as possible on this day, since "there is no other day on which Allah frees a larger number of His slaves from the Fire of Hell than the Day of Arafah." [Sahih Muslim]
The Prophet (sallallahu alaihi wa sallam) said:
خَيْرُ الدُّعَاءِ دُعَاءُ يَوْمِ عَرَفَةَ وَخَيْرُ مَا قُلْتُ أَنَا وَالنَّبِيُّونَ مِنْ قَبْلِي لَا إِلَهَ إِلَّا اللَّهُ وَحْدَهُ لَا شَرِيكَ لَهُ لَهُ الْمُلْكُ وَلَهُ الْحَمْدُ وَهُوَ عَلَى كُلِّ شَيْءٍ قَدِيرٌ
"The best supplication is on the day of Arafa, and the best remembrance that I and the prophets before me (made) is: "There is no god but Allah, the only true God, who has no partner. To Him belongs the kingdom (of the universe) and to Him all praises are due. And He has the power to do every thing." [Tirmidhi]
. The Prophet also said,
الْحَجُّ عَرَفَةُ فَمَنْ أَدْرَكَ لَيْلَةَ عَرَفَةَ قَبْلَ طُلُوعِ الْفَجْرِ مِنْ لَيْلَةِ جَمْعٍ فَقَدْ تَمَّ حَجُّهُ
“The Ḥajj is itself ‘Arafāt. Whoever reaches the night of ‘Arafāt before the rising of the sun at dawn the following day has completed his pilgrimage.”
Make a note of this day on your calendar, so that you remember to celebrate it by fasting and making dhikr, dua and istighfar.