Sunan an-Nasa'i 1940
سنن النسائي#1940SahihIt was narrated that Al-Musayyab bin Rafi' said:"I heard Al-Bara' bin 'Azib say: The Messenger of Allah said: 'whoever follows a Janazah until the prayer is offered, he will have one Qirat of reward and whoever walks with the funeral until (the body) is buried will have two Qirats of reward, and a Qirat is like Uhud
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 ZaiIsnaad Sahih
In-book reference: 21:123