(1) باب مَا يُبَاحُ لِلْمُحْرِمِ بِحَجٍّ أَوْ عُمْرَةٍ وَمَا لاَ يُبَاحُ وَبَيَانِ تَحْرِيمِ الطِّيبِ عَلَيْهِ
Ibn 'Abbas (Allah be pleased with both of them) reported:
I heard Allah's Messenger (ﷺ) say as he was delivering an address: So far as the trousers are concerned, one who does not find lower garment, he may wear them; as also socks, he may wear them who does not find shoes. It concerns the Muhrim.
Reference: Sahih Muslim 1178 a
In-book reference: Book 15, Hadith 4
USC-MSA web (English) reference(deprecated numbering scheme): Book 7, Hadith 2650