From Sahih Muslim (Hadith 2216):
It is narrated on the authority of 'Abd al-Rahman b. Abu Laila that Zaid used to recite four takbirs on our funerals and he recited five takbirs on one funeral. I asked him the reason (for this variation), to which he replied:The Messenger of Allah (ﷺ) recited thus
Reference: Muslim 2216