Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.099.

It is confirmed that the Prophet (peace be upon him) did not fast on the Day of Arafah. The Prophet (peace be upon him) said: “Verily the Day of Arafah, the Day of Sacrifice (Yaum al-Nahr), and Ayam Tashriq (the 10th, 11th and 12th of Zhul-Hijjah) are our days of festivities. These are the days of eating and drinking.” It is also established that the Prophet (peace be upon him) forbade fasting on the Day of Arafah while at Arafah (for pilgrimage).

This has led most of the scholars to conclude that in fact not fasting on the Day of Arafah is desirable, so that a pilgrim should be strong enough to devote himself wholeheartedly to worship and supplications.

Some of the ahadith that encourage fasting on the Day of Arafah concern the persons who are not staying at Arafah as pilgrims performing Hajj.