Praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
The Day of `Arafah is amongst the best days in the sight of Allah and there is a Prophetic narration encouraging Muslims to observe fast on it. The Messenger of Allah(PBUH) said: " I seek from Allah that fasting on the day of 'Arafa may atone for the sins of the preceding and the coming years." {Transmitted by Muslim}.
In addition, it is recommended to fast the Day of `Arafah even if it falls on a Jumu`ah (Friday) because this is excluded from the reprehensibility of singling out Friday with fasting. Actually, singling out Friday with fasting is reprehensible in case of optional fasting. However, if the person is used to fasting, such as fasting one day and not fasting the next and so on, and it fell on Friday, or it was Sunnah fasting, such as fasting `Arafah or `Ashura`, then it isn`t reprehensible to single out Friday with fasting.
Ar-Ramli, a Shafie scholar, said: "It is disliked to single out Friday with fasting based on the authentic Hadith in which the Prophet (PBUH) said: " None of you must fast on Friday unless he fasts the day before or the day after." However, this isn`t reprehensible in case the person is used to observe fast, such as fasting one day and breaking fast the next or in case of fasting the day before Friday and the day after." {Nehayat Al-Mohtaj, Vol.3:Page209}. Also, check {Tohfat Al-Mohtaj by Ibn Hajar Al-Haitami.
In conclusion, it is recommended to fast the Day of `Arafah even if it falls on Friday and this isn`t disliked even if the person fasted the day before or didn`t because the Day of `Arafah has a specific time. And Allah the Almighty knows best.