صحيح البخاري
From Sahih Bukhari (Hadith 1766):
Narrated Ibn `Abbas:Staying at Al-Mahassab is not one of the ceremonies (of Hajj), but Al-Mahassab is a place where Allah's Messenger (ﷺ) camped (during his Hajjat-al-Wida)
Reference: Bukhari 1766