Musnad Ahmad 30:2978

Yahya narrated to us, he said: Ibn Abi Dhi'b narrated to us, he said: Salih, the freed slave of al-Taw'amah, narrated to us, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him, who said: "Whoever washes a dead person, let him perform ghusl (ritual bath)."