Sunan an Nasai
5381
Sahih+2

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

SahihAbu Ghuddah
SahihAl-Albani