It was narrated that Al-Musayyab bin Rafi' said: "I heard Al-Bara' bin 'Azib say: The Messenger of Allah (ﷺ) 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."'
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا عَبْثَرٌ، عَنْ بُرْدٍ، أَخِي يَزِيدَ بْنِ أَبِي زِيَادٍ عَنِ الْمُسَيَّبِ بْنِ رَافِعٍ، قَالَ سَمِعْتُ الْبَرَاءَ بْنَ عَازِبٍ، يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ تَبِعَ جَنَازَةً حَتَّى يُصَلَّى عَلَيْهَا كَانَ لَهُ مِنَ الأَجْرِ قِيرَاطٌ وَمَنْ مَشَى مَعَ الْجَنَازَةِ حَتَّى تُدْفَنَ كَانَ لَهُ مِنَ الأَجْرِ قِيرَاطَانِ وَالْقِيرَاطُ مِثْلُ أُحُدٍ " .
sunnah.com