Musnad Ahmad 30:3261

Muhammad ibn Ja‘far narrated to us, he said: ‘Awf and Ishaq—meaning Ibn Yusuf al-Azraq—narrated to us, he said: ‘Awf informed us—the meaning is the same—from Muhammad, from Abu Hurairah, that the Messenger of Allah (ﷺ) said: "Whoever follows the funeral procession of a Muslim, seeking reward, and remains with it until the prayer is performed over it and the burial is completed, he returns with two qirats of reward, each qirat being like Uhud. And whoever prays over it and returns before it is buried, he returns with one qirat." Ishaq said: "Believing and seeking reward." And he said: "If he returns before it is placed in the grave, he returns with one qirat."