Mishkat al-Masabih 18 The Offices of Commander and Qadi كتاب الإمارة والقضاء 71

وَعَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو وَأَبِي هُرَيْرَةَ قَالَا: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِذَا حَكَمَ الْحَاكِمُ فَاجْتَهَدَ فَأَصَابَ فَلَهُ أَجْرَانِ وَإِذَا حَكَمَ فَاجْتَهَدَ فَأَخْطَأَ فلهُ أجرٌ واحدٌ»

‘Abdallah b. ‘Amr and Abu Huraira reportad God’s Messenger as saying, “When a judge gives a decision having tried his best to decide correctly and is right, he will have a double reward; and when he gives a decision having tried his best to decide correctly and is wrong, he will have a single reward.” (Bukhari and Muslim.)