Musnad Abu Ya'la al-Mawsili 153:11

And from al-Zuhri, he heard Salim narrating from his father: That the Prophet (peace and blessings of Allah be upon him) was asked: "What garments should the *muhrim* (one in the state of ihram) wear?" 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 below the ankles."