(15) باب لُبْسِ الْخُفَّيْنِ لِلْمُحْرِمِ إِذَا لَمْ يَجِدِ النَّعْلَيْنِ
Narrated Ibn `Abbas:
I heard the Prophet (ﷺ) delivering a sermon at `Arafat saying, "If a Muhrim does not find slippers, he could wear Khuffs (socks made from thick fabric or leather, but he has to cut short the Khuffs below the ankles), and if he does not find an Izar (a waist sheet for wrapping the lower half of the body) he could wear trousers."
Reference: Sahih al-Bukhari 1841
In-book reference: Book 28, Hadith 21
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 29, Hadith 67