Hadith: I heard the Prophet (may Allah's peace and blessings be upon him) delivering a sermon at ‘Arafāt, in which he said: Whoever does not find slippers or sandals (Na‘l) may wear leather socks (Khuff), and whoever does not find a waist sheet (Izār) may wear pants (Sirwāl). He meant the pilgrim in the state of Ihrām

عن عبد الله بن عباس رضي الله عنهما قال: «سمعت رسول الله صلى الله عليه وسلم يخطب بِعَرَفَاتٍ: من لم يَجِدْ نَعْلَيْنِ فَلْيَلْبَسِ الخُفَّيْنِ، ومن لَمْ يَجِدْ إِزَارًا فَلْيَلْبَسْ السَّرَاوِيلَ -للمحرم-».
[صحيح] - [رواه البخاري]

‘Abdullāh ibn ‘Abbās (may Allah be pleased with him) reported: I heard the Prophet (may Allah's peace and blessings be upon him) delivering a sermon at ‘Arafāt, in which he said: "Whoever does not find slippers or sandals (Na‘l) may wear leather socks (Khuff), and whoever does not find a waist sheet (Izār) may wear pants (Sirwāl).' He meant the pilgrim in the state of Ihrām."
Sahih/Authentic. - [Al-Bukhari]

Explanation

Ibn ‘Abbās (may Allah be pleased with him) reports that the Prophet (may Allah's peace and blessings be upon him) addressed the people on the Day of ‘Arafah while he was in ‘Arafat. He permitted them to wear Khuff in case they cannot find sandals or slippers, without mentioning cutting the socks below the ankles. He also permitted them to wear Sirwāl for the one who cannot find an Izār, without stipulating cutting the Sirwāl open, as a form of alleviation from Allah, the Exalted, the Most Wise.