I heard the Prophet ﷺ delivering a sermon at ʿArafat 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."  

سَمِعْتُ النَّبِيَّ ﷺ يَخْطُبُ بِعَرَفَاتٍ مَنْ لَمْ يَجِدِ النَّعْلَيْنِ فَلْيَلْبَسِ الْخُفَّيْنِ وَمَنْ لَمْ يَجِدْ إِزَارًا فَلْيَلْبَسْ سَرَاوِيلَ لِلْمُحْرِمِ  

Messenger of Allah ﷺ was asked what sort of clothes a Muhrim should wear. He replied, "He should not wear a shirt, turbans, trousers, a hooded cloak, or a dress perfumed with saffron or Wars; and if slippers are not available he can wear Khuffs (socks made from thick fabric or leather) but he should cut them so that they reach below the ankles.  

عَنْ عَبْدِ اللَّهِ ؓ سُئِلَ رَسُولُ اللَّهِ ﷺ مَا يَلْبَسُ الْمُحْرِمُ مِنَ الثِّيَابِ فَقَالَ لاَ يَلْبَسِ الْقَمِيصَ وَلاَ الْعَمَائِمَ وَلاَ السَّرَاوِيلاَتِ وَلاَ الْبُرْنُسَ وَلاَ ثَوْبًا مَسَّهُ زَعْفَرَانٌ وَلاَ وَرْسٌ وَإِنْ لَمْ يَجِدْ نَعْلَيْنِ فَلْيَلْبَسِ الْخُفَّيْنِ وَلْيَقْطَعْهُمَا حَتَّى يَكُونَا أَسْفَلَ مِنَ الْكَعْبَيْنِ