Abu Salman the mu'adhdhin narrates: I prayed a funeral prayer with Sayyiduna Zayd bin Arqam (may Allah be pleased with him), and he said five takbirs. I asked: "Was this by mistake or deliberately?" He said: "Rather deliberately; indeed the Prophet (peace and blessings be upon him) used to pray it (the funeral prayer) this way."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4975