Question:  What is the reward for the righteous jurist who is just in his judgment?

Answer:  Allah and his messenger s.a.w has mentioned many virtues for the righteous jurist who strives best to achieve justice.

Allah s.w.t says: “O you who have believed, be persistently standing firm in justice, witnesses for Allah, even if it
be against yourselves or parents and relatives. Whether one is rich or poor, Allah is more worthy
of both. So follow not [personal] inclination, lest you not be just. And if you distort [your
testimony] or refuse [to give it], then indeed Allah is ever, with what you do, Acquainted” (Surah Al-Maida
4:135)

Also the Prophet s.a.w narrated in the following Hadith:

Narrated ‘Amr bin Al-‘As r.a: “That he heard Allah’s Apostle saying, “If a judge gives a verdict according to the best of his knowledge and his verdict is correct (i.e. agrees with Allah and His Apostle’s verdict) he will receive a double reward, and if he gives a verdict according to the best of his knowledge and his verdict is wrong, (i.e. against that of Allah and His Apostle) even then he will get a reward .”

Reference: [1] Sahih al-Bukhari:7352