Sunan Ibn Majah
1505
Sahih+3

It was narrated that ‘Abdur-Rahman bin Abi Laila said:“Zaid bin Arqan used to say the Takbir four times in the funeral prayer, and he said the Takbir five times for one funeral. I asked him (about that) and he said: ‘The Messenger of Allah (ﷺ) used to do that.’”

SahihAl-Albani
SahihMuhammad Fouad Abd al-Baqi