Musnad Abu Ya'la al-Mawsili 153:192

Muhammad ibn Bashar narrated to us, Abu 'Amir al-'Aqdi narrated to me, Ayyub ibn Thabit al-Madani narrated to us, he said: I heard Khalid ibn Kaysan say: I was sitting with Ibn 'Umar when a youth passed by dragging his garment. He said to me: "Call him, call him." I called him. He said: He said to him: "Raise your lower garment." He raised it to above his heel. Ibn 'Umar said: "Thus did the Messenger of Allah (may Allah bless him and grant him peace) wear his lower garment," or he said: "Thus did the Messenger of Allah (may Allah bless him and grant him peace) command us to wear our lower garments."