Abdul Rahman bin Abi Layla narrates: I prayed the funeral prayer behind Sayyiduna Zayd bin Arqam (may Allah be pleased with him) over a deceased, and he said four takbirs; then I prayed behind him over another, and he said five takbirs. I asked him about it, and he said: "The Messenger of Allah (peace and blessings be upon him) also used to say the takbirs in this way."
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4957