What is the ruling concerning the fasting the day of Arafah

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Fasting on the day of Arafah is a supererogatory act of worship. The Prophet Muhammad urged us to fast on this day.Abu Qatadah narrated that the Prophet was asked about observing the fast on the day of ‘Arafah, and he replied: “Fasting on the day of ‘Arafah wipes out the sins of two years: the previous year and the coming year.” [Muslim, Abu Daawood, An-Nasaa'i and Ibn Maajah]

The Prophet was also asked about fasting on the day of ‘Ashoora’ (Tenth day of Muharram) and he replied: "Fasting on the day of ‘Ashooraa’ wipes out the sins of the previous year.” [Muslim, Abu Daawood, An-Nasaa'i and Ibn Maajah]

Moreover, when he was asked about fasting on Monday, he said: "This (Monday) is the day on which I was born, and the day on which I was commissioned for Prophethood, and the day I received the first revelation”.

As mentioned above, fasting on the day of ‘Arafah is only for the non-pilgrims. But, in regard to those who are performing Hajj, it is better for them not to fast on this day so that they can be strong in order to carry out the entire rituals of that day such as supplicating, staying in ‘Arafah, going to Muzdalifah and staying overnight there and the like.

Allah knows bset.