Musnad Ahmad 25:379

Ali ibn Asim narrated to us, from Ata ibn al-Sa'ib, from Sa'id ibn Jubayr, from Ibn Abbas, who said: The Messenger of Allah, peace and blessings of Allah be upon him, commanded on the day of Uhud regarding the martyrs that the iron (armor) and the skins (leather gear) be removed from them. And he said: "Bury them with their blood and their garments."