Sahih Muslim Book 7, Hadith Number 2650.

Chapter : What is permitted for the Muhrim (wearer of Ihram) in Hajj and Umra, what is not permissible and forbiddance of the use of perfume.

Ibn ‘Abbas (Allah be pleased with both of them) reported: I heard Allah’s Messenger (may peace be upon him) 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.