It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "A ritual bath is not obligatory upon you for washing your deceased when you wash him. He is a pure Muslim believer, and a Muslim is not impure; it is sufficient for you to wash your hands."
This is weak, and the blame for it lies, I think, with Abu Shaybah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1462