It was narrated from 'Amr bin 'As that he heard the Messenger of Allah ﷺ say:
“When the judge passes a judgement and does his best and gets it right, he will have two rewards, and if he passes a judgement and does his best and gets it wrong, he will have one reward.”
Yazid (one of narrators) said : “So I Narrated it to Abu Bakr bin 'Amr bin Hazm. He said: 'This is how it was narrated to me by Abu Salamah from Abu Hurairah.'”

حَدَّثَنَا هِشَامُ بْنُ عَمَّارٍ، حَدَّثَنَا عَبْدُ الْعَزِيزِ بْنُ مُحَمَّدٍ الدَّرَاوَرْدِيُّ، حَدَّثَنَا يَزِيدُ بْنُ عَبْدِ اللَّهِ بْنِ الْهَادِ، عَنْ مُحَمَّدِ بْنِ إِبْرَاهِيمَ التَّيْمِيِّ، عَنْ بُسْرِ بْنِ سَعِيدٍ، عَنْ أَبِي قَيْسٍ، - مَوْلَى عَمْرِو بْنِ الْعَاصِ - عَنْ عَمْرِو بْنِ الْعَاصِ، أَنَّهُ سَمِعَ رَسُولَ اللَّهِ ﷺ يَقُولُ " إِذَا حَكَمَ الْحَاكِمُ فَاجْتَهَدَ فَأَصَابَ فَلَهُ أَجْرَانِ وَإِذَا حَكَمَ فَاجْتَهَدَ فَأَخْطَأَ فَلَهُ أَجْرٌ " . قَالَ يَزِيدُ فَحَدَّثْتُ بِهِ أَبَا بَكْرِ بْنَ عَمْرِو بْنِ حَزْمٍ، فَقَالَ هَكَذَا حَدَّثَنِيهِ أَبُو سَلَمَةَ، عَنْ أَبِي هُرَيْرَة.َ