Musnad Ahmad 30:652

'Abd al-Razzaq narrated to us, Ma'mar narrated to us, from Yahya ibn Abi Kathir, from a man who is called Abu Ishaq, from Abu Hurayrah, who said: The Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever washes a dead person, let him perform ghusl (a full ritual bath)."