Musannaf Ibn Abi Shayba 16:604

Abu Bakr narrated to us, he said: Ubayd Allah ibn Musa narrated to us, he said: Musa ibn Ubaynah informed us, from Iyas ibn Salamah, from his father, from Uthman ibn Affan: His lower garment (izar) used to reach the middle of his shins. It was said to him regarding that, and he said: "This is the way my beloved wore his lower garment," meaning the Prophet, peace be upon him.