أَخْبَرَنَا إِسْحَاقُ بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا عَبْدُ الرَّزَّاقِ، قَالَ أَنْبَأَنَا مَعْمَرٌ، عَنْ سُفْيَانَ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ أَبِي بَكْرِ، {بْنِ} مُحَمَّدِ بْنِ عَمْرِو بْنِ حَزْمٍ عَنْ أَبِي سَلَمَةَ، عَنْ أَبِي هُرَيْرَةَ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " إِذَا حَكَمَ الْحَاكِمُ فَاجْتَهَدَ فَأَصَابَ فَلَهُ أَجْرَانِ وَإِذَا اجْتَهَدَ فَأَخْطَأَ فَلَهُ أَجْرٌ ".
It was narrated that Abu Hurairah said: "The Messenger of Allah [SAW] said: 'If a judge passes judgment and strives to reach the right conclusion and gets it right, he will have two rewards; if he strives to reach the right conclusion but gets it wrong, he will still have one reward." Translation Not Available
Book Ref: Sunan An Nisai Book 49 Hadith 5381
Web Ref: Sunan An Nisai Vol 6 Book 49 Hadith 5383