Narrated Ibn ‘Abbas:
I heard the Prophet delivering a sermon at ‘Arafat saying, “If a Muhrim does not find slippers, he could wear Khuffs (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.”
Sahih Bukhari, Volume 3, Book29, Number 67