Volume 9, Book 92, Number 450:
Narrated ‘Amr bin Al-‘As:
That he heard Allah’s Apostle saying, “If a judge gives a verdict according to the best of his know –
ledge 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 .”