The Book of Funerals
21/77. Chapter:
Supplication
Sunan an-Nasai
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنِ ابْنِ شِهَابٍ، عَنْ أَبِي أُمَامَةَ، أَنَّهُ قَالَ السُّنَّةُ فِي الصَّلاَةِ عَلَى الْجَنَازَةِ أَنْ يَقْرَأَ فِي التَّكْبِيرَةِ الأُولَى بِأُمِّ الْقُرْآنِ مُخَافَتَةً ثُمَّ يُكَبِّرَ ثَلاَثًا وَالتَّسْلِيمُ عِنْدَ الآخِرَةِ .
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."
Reference : Sunan an-Nasa'i 1989In-book reference : Book 21, Hadith 172English translation : Vol. 3, Book 21, Hadith 1991