The Book of Funerals
21/56. Chapter:
The Place For Pedestrians When Following Janazah
Sunan an-Nasai
أَخْبَرَنَا إِسْحَاقُ بْنُ إِبْرَاهِيمَ، وَعَلِيُّ بْنُ حُجْرٍ، وَقُتَيْبَةُ، عَنْ سُفْيَانَ، عَنِ الزُّهْرِيِّ، عَنْ سَالِمٍ، عَنْ أَبِيهِ، أَنَّهُ رَأَى رَسُولَ اللَّهِ صلى الله عليه وسلم وَأَبَا بَكْرٍ وَعُمَرَ رَضِيَ اللَّهُ عَنْهُمَا يَمْشُونَ أَمَامَ الْجَنَازَةِ .
It was narrated from Salim: That his father saw the Messenger of Allah, Abu Bakr and 'Umar, may Allah be pleased with them, walking in front of the Janazah.
Reference : Sunan an-Nasa'i 1944In-book reference : Book 21, Hadith 127English translation : Vol. 3, Book 21, Hadith 1946