That he heard Messenger of Allah ﷺ saying, "If a judge gives a verdict according to the best of his knowledge and his verdict is correct (i.e. agrees with Allah and His Apostle's verdict) he will receive a double reward, and if he gives a verdict according to the best of his knowledge and his verdict is wrong, (i.e. against that of Allah and His Apostle) even then he will get a reward ."  

أَنَّهُ سَمِعَ رَسُولَ اللَّهِ ﷺ يَقُولُ إِذَا حَكَمَ الْحَاكِمُ فَاجْتَهَدَ ثُمَّ أَصَابَ فَلَهُ أَجْرَانِ وَإِذَا حَكَمَ فَاجْتَهَدَ ثُمَّ أَخْطَأَ فَلَهُ أَجْرٌ قَالَ فَحَدَّثْتُ بِهَذَا الْحَدِيثِ أَبَا بَكْرِ بْنَ عَمْرِو بْنِ حَزْمٍ فَقَالَ هَكَذَا حَدَّثَنِي أَبُو سَلَمَةَ بْنُ عَبْدِ الرَّحْمَنِ عَنْ أَبِي هُرَيْرَةَ وَقَالَ عَبْدُ الْعَزِيزِ بْنُ الْمُطَّلِبِ عَنْ عَبْدِ اللَّهِ بْنِ أَبِي بَكْرٍ عَنْ أَبِي سَلَمَةَ عَنِ النَّبِيِّ ﷺ مِثْلَهُ