Musnad Abu Ya'la al-Mawsili 4:32

Suwayd ibn Sa'id narrated to us, Sufyan ibn 'Uyaynah narrated to us, from Yazid ibn Khusayfah, from al-Sa'ib ibn Yazid, from a man from Banu Tamim who is called Mu'adh: That the Messenger of Allah, may Allah bless him and grant him peace, wore two coats of mail on the day of Uhud.