Sunan an-Nasa'i, Hadith 2680 ⓘ
It was narrated from Ibn 'Umar: That the Prophet said "If a Muhrim cannot find sandals then let him wear Khuffs, and cut them, so that they come lower than the ankles.''
أَخْبَرَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا هُشَيْمٌ، قَالَ أَنْبَأَنَا ابْنُ عَوْنٍ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، رضى الله عنهما عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " إِذَا لَمْ يَجِدِ الْمُحْرِمُ النَّعْلَيْنِ فَلْيَلْبَسِ الْخُفَّيْنِ وَلْيَقْطَعْهُمَا أَسْفَلَ مِنَ الْكَعْبَيْنِ " .
also referenced under: Book 24, Hadith 0 (In-Book) & Volume 3, Book 24, Hadith 2681 (DarusSalam)