Jami` at-Tirmidhi Book 10, Hadith 62
"The Prophet recited Fatihatil-Kitab for a funeral (prayer)." (Da'if Jiddan)
"I heard the Messenger of Allah, while he was performing Salat for a deceased person. I could hear him saying in his prayer: (Allahummagfir lahu, war hamhu, waghsilhu bil-baradi (waghsilhu) kama yughsaluth-thawb) 'O Allah! Forgive him, have mercy upon him, and wash him with (snow or ice) (and wash him) just as a garment is washed.'"
"Ibn Abbas performed Salat for a funeral and he recited Fatihatil-Kitab. So I asked him about it and he said: 'It is from the Sunnah' or, 'From the completeness of the Sunnah.'"