Jami` at-Tirmidhi Book 10, Hadith 59
"Zaid bin Arqam would say four Takbir for our funerals. (Once) he said five Takbir for a funeral so we asked him about that and he said: 'The Messenger of Allah would say those Takbir.'"
"The Prophet prayed and in the funeral prayer he for An-Najashi, said four Takbir."
from his father who said: "When the Messenger of Allah would perform the Salat for the funeral he would said: (Allahammaghfir li-hayyina wa mayyittina, wa shahidina wa gha'ibina, wa saghirina wa kabirina, wa dhakarina wa unthana) 'O Allah! Forgive our living and our deceased, our present and our absent, our young and our old, our male and our female.'"