Musnad Abu Ya'la al-Mawsili 111:17

Abu Ya'la informed us, he said: It was read to Bishr ibn al-Walid, Abu Yusuf informed you, from Ishaq ibn Rashid, from al-Zuhri, from Abdullah ibn Tha'labah al-Udhri, from the Messenger of Allah, may Allah bless him and grant him peace, that he said regarding the martyrs of the day of Uhud: "I am a witness over these people on the Day of Resurrection. Wrap them in their wounds and their blood, and do not wash them."