Hadith 14:4
Narrated 'Amr bin al-'Aas (RA):
He heard Allah's Messenger (ﷺ) say, "When a judge gives a ruling, having tried his best to decide correctly, and is right (in his decision), he will have a double reward; and when he gives a ruling having tried his best to decide correctly, and is wrong (in his decision), he will have a single reward." [Agreed upon].
وَعَنْ عَمْرِو بْنِ الْعَاصِ - رضى الله عنه - أَنَّهُ سَمِعَ رَسُولَ اَللَّهِ - صلى الله عليه وسلم -يَقُولُ: { "إِذَا حَكَمَ اَلْحَاكِمُ, فَاجْتَهَدَ, ثُمَّ أَصَابَ, فَلَهُ أَجْرَانِ. وَإِذَا حَكَمَ, فَاجْتَهَدَ, ثُمَّ أَخْطَأَ, فَلَهُ أَجْرٌ" } مُتَّفَقٌ عَلَيْهِ
Original Reference: Bulugh al-Maram 1400