What following a funeral through is worth
He compared the measure to something they could see.
مَنِ اتَّبَعَ جَنَازَةَ مُسْلِمٍ إِيمَانًا وَاحْتِسَابًا، وَكَانَ مَعَهُ حَتَّى يُصَلَّى عَلَيْهَا، وَيَفْرُغَ مِنْ دَفْنِهَا، فَإِنَّهُ يَرْجِعُ مِنَ الأَجْرِ بِقِيرَاطَيْنِ
Mani-ttabaʿa janāzata muslimin īmānan wa-ḥtisāban, wa kāna maʿahu ḥattā yuṣallā ʿalayhā wa yafrugha min dafnihā, fa-innahu yarjiʿu mina-l-ajri bi-qīrāṭayn
“Whoever follows a Muslim's funeral out of faith and seeking the reward, and stays with it until the prayer is done and the burial is finished, comes back with two carats of reward.”
Where this comes from
Each carat is like Uhud. Whoever prays and then leaves before the burial comes back with one. The whole difference is in staying to the end, when there is nothing left to do but stand there.
The full narration
Narrated Abu Huraira: Allah's Messenger (ﷺ) said, "(A believer) who accompanies the funeral procession of a Muslim out of sincere faith and hoping to attain Allah's reward and remains with it till the funeral prayer is offered and the burial ceremonies are over, he will return with a reward of two Qirats. Each Qirat is like the size of the (Mount) Uhud. He who offers the funeral prayer only and returns before the burial, will return with the reward of one Qirat only
Source
Ṣaḥīḥ al-Bukhārī · 47
- Agreed upon as authentic (al-Bukhārī / Muslim)