"The Prophet prayed and in the funeral prayer he for An-Najashi, said four Takbir."  

أَنَّ النَّبِيَّ ﷺ صَلَّى عَلَى النَّجَاشِيِّ فَكَبَّرَ أَرْبَعًا قَالَ وَفِي الْبَابِ عَنِ ابْنِ عَبَّاسٍ وَابْنِ أَبِي أَوْفَى وَجَابِرٍ وَيَزِيدَ بْنِ ثَابِتٍ وَأَنَسٍ  

"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.'"  

كَانَ رَسُولُ اللَّهِ ﷺ يُكَبِّرُهَا