Hamam bin Munabbih همام بن منبه بن كامل · The Book of Funerals

"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."'