From Sahih Bukhari (Hadith 1841):
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: Bukhari 1841