'Amr b. al-'As reported that he heard Allah's Messenger (ﷺ) 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.
This hadith has been narrated on the authority of Abu Huraira with another chain of transmitters.
This hadith has been transmitted on the authority of Usama b. al-Had al-Laithi.