Musnad Ahmad 1119:31

'Abd al-Rahman ibn Mahdi narrated to us, from Mu'awiyah, from 'Abd al-Rahman ibn Jubayr, from his father, from 'Awf ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) prayed over a deceased person. He said: I understood from his prayer over him: "O Allah, forgive him, and have mercy on him, and wash him with water, and snow, and cleanse him of sins, just as You cleansed the white garment of filth."