In a letter to Malik Ashtar, Imam Ali (AS) wrote:

For adjudicating between people, choose your best individuals! The one who is tolerant and various issues do not put him under pressure, and the enmity and vindictiveness of both sides does not make him angry or irritable. And he does not insist on his errors, and when he finds out about his mistake, it is not difficult for him to admit to it, and his soul is not inclined to greediness [1].

[1] Nahjul Balaghah, Letter 53

Source: en.shafaqna.com