Sahih al-Bukhari 1843
Sahih al-Bukhari · Book 28: Penalty of Hunting while on Pilgrimage · If an Izar is not available, one can wear trousers
Narrated Ibn `Abbas:
حَدَّثَنَا آدَمُ ، حَدَّثَنَا شُعْبَةُ ، حَدَّثَنَا عَمْرُو بْنُ دِينَارٍ ، عَنْ جَابِرِ بْنِ زَيْدٍ ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ خَطَبَنَا النَّبِيُّ صلى الله عليه وسلم بِعَرَفَاتٍ فَقَالَ " مَنْ لَمْ يَجِدِ الإِزَارَ فَلْيَلْبَسِ السَّرَاوِيلَ، وَمَنْ لَمْ يَجِدِ النَّعْلَيْنِ فَلْيَلْبَسِ الْخُفَّيْنِ " .
The Prophet (ﷺ) delivered a sermon at `Arafat and said, "Whoever does not get an Izar can wear trousers, and whoever cannot get a pair of shoes can wear Khuffs (socks made from thick fabric or leather)."