Sunan an-Nasa'i, Hadith 2679 ⓘ
It was narrated that Ibn 'Abbas said: "I heard the Messenger of Allah say; 'If you cannot find an Izar then wear pants, and if you cannot find sandals then wear khuffs, but cut them so that they come lower than the ankles.
أَخْبَرَنَا إِسْمَاعِيلُ بْنُ مَسْعُودٍ، قَالَ حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، قَالَ أَنْبَأَنَا أَيُّوبُ، عَنْ عَمْرٍو، عَنْ جَابِرِ بْنِ زَيْدٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " إِذَا لَمْ يَجِدْ إِزَارًا فَلْيَلْبَسِ السَّرَاوِيلَ وَإِذَا لَمْ يَجِدِ النَّعْلَيْنِ فَلْيَلْبَسِ الْخُفَّيْنِ وَلْيَقْطَعْهُمَا أَسْفَلَ مِنَ الْكَعْبَيْنِ " .
also referenced under: Book 24, Hadith 0 (In-Book) & Volume 3, Book 24, Hadith 2680 (DarusSalam)