Jami` at-Tirmidhi Book 10, Hadith 63
"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.'"
"The Prophet recited Fatihatil-Kitab for a funeral (prayer)." (Da'if Jiddan)
"When Malik bin Hubairah performed Salat for a funeral and the people were few he would divide them into three groups (rows) then say: 'The Messenger of Allah said: "For whomever three rows perform Salat, then it is granted."