It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both): "A ritual bath is not obligatory upon you for washing your deceased, once you have washed him. Your deceased is a pure believer, not impure; it is sufficient for you to wash your hands."
This has also been narrated as marfu' (from the Prophet), but its being marfu' is not authentic.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1461