وَعَنْ أَبِي هُرَيْرَةَ رضى الله عنه
أَنَّ اَلنَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ -«نَهَى عَنْ صَوْمِ يَوْمِ عَرَفَةَ بِعَرَفَةَ»
The Messenger of Allah (sallallahu alayhi wa sallam) forbade fasting on the day of Arafah for the one who is actually at Arafah (i.e. performing Hajj). Related by the five Imams except for At-Tirmidhi. Ibn Khuzaimah and al-Hakim graded it as Sahih.