حَدَّثَنَا يَحْيَى بْنُ يَحْيَى التَّمِيمِيُّ، أَخْبَرَنَا عَبْدُ الْعَزِيزِ بْنُ مُحَمَّدٍ، عَنْ يَزِيدَ بْنِ عَبْدِ، اللَّهِ بْنِ أُسَامَةَ بْنِ الْهَادِ عَنْ مُحَمَّدِ بْنِ إِبْرَاهِيمَ، عَنْ بُسْرِ بْنِ سَعِيدٍ، عَنْ أَبِي قَيْسٍ، مَوْلَى عَمْرِو بْنِ الْعَاصِ عَنْ عَمْرِو بْنِ الْعَاصِ، أَنَّهُ سَمِعَ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏"‏ إِذَا حَكَمَ الْحَاكِمُ فَاجْتَهَدَ ثُمَّ أَصَابَ فَلَهُ أَجْرَانِ ‏.‏ وَإِذَا حَكَمَ فَاجْتَهَدَ ثُمَّ أَخْطَأَ فَلَهُ أَجْرٌ ‏"‏ ‏.‏

'Amr b. al-'As reported that he heard Allah's Messenger (PBUH) as saying: When a judge gives a decision, having tried his best to decide correctly and is right, there are two rewards for him; and if he gave a judgment after having tried his best (to arrive at a correct decision) but erred, there is one reward for him. Translation Not Available

Book Ref: Sahih Muslim Book 30 Hadith 4261
Web Ref:  Sahih Muslim Book 18 Hadith 1716 a