Musnad Abu Ya'la al-Mawsili 153:74

And from Salim, from his father: The Prophet, may Allah bless him and grant him peace, was asked, "What garments should the Muhrim (pilgrim in Ihram) wear?" He said, "Do not wear the shirt, nor trousers, nor turbans, nor hooded cloaks (burnus), nor any garment touched by wars (a type of dye) or saffron. And do not wear leather socks (khuffayn), unless a man does not have sandals; then let him cut them below the ankles."