Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.057B.
Section : Making Ghusl at Mount ‘Arafah.
Such an act is preferred while one stops there during the hajj. Malik ibn Nafa’ reported that Ibn ‘Umar used to do so before embarking upon the hajj, upon entering Makkah, and while stopping at ‘Arafah.