Sunan an-Nasa'i 1989
سنن النسائي#1989Sahih(It was narrated that Abu Umamah said:"The Sunnah, when offering the funeral prayer, is to recite Umm Al-Qur'an) the Exxence of the Qur'an) quietly in the first Takbir, Then to say three (more) Takbir and to say the Taslim after the last one
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih
Al-AlbaniSahih
Zubair Ali ZaiSahih
In-book reference: 21:172