Musnad Abu Ya'la al-Mawsili 153:119

And from his father, that the Messenger of Allah (may Allah bless him and grant him peace) was asked: "What may the *muhrim* (pilgrim in state of ihram) wear of garments?" He said: "He shall not wear the shirt, nor the turban, nor the hooded cloak (*burnus*), nor the trousers, nor a garment touched by saffron or *wars* (a yellow dye), nor leather socks, except for one who does not find sandals. So whoever does not find sandals, let him cut them until they are below the ankles."