From Sahih Muslim (Hadith 2794):
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: Muslim 2794