It was narrated from Abu Hurairah that:
The Prophet [SAW] said: "Whoever follows the funeral procession of a Muslim out of faith and in the hope of reward, then offers the funeral prayer for him and waits until he is placed in his grave, then he will have two Qirats, each of which is like Mount Uhud. Whoever offers the funeral prayer for him then returns, he will have one Qirat."