It depends on what you mean by 'judge'. If it were impermissible to judge others, there would be no judiciary, and no criminals would be brought to court and justice would not be done for victims of crimes. There is a fine line between being bigoted or prejudiced, and using what insight Allah (swt) has blessed you with to assess people. There are many ahadith about the necessity for choosing your spouse carefully or choosing your friends carefully. This requires a judgement of someone's personality. If we did not judge at all, then people could have criminals for friends and non-believers for spouses. Children would be raised with no moral compass and would be allowed to do whatever they wanted because the parents would feel they were judging them if they tried to establish boundaries for them. When seeking knowledge, a person would not 'judge' between good teachers and bad teachers, and would simply go to anybody to try to study. If by 'judge' you mean 'condemn someone without evidence', then that is not permissible; or even if someone is a criminal, maybe we should not look down on them and think we are superior to them, because we don't know what their circumstances were in life that led them to commit crimes. Nevertheless, they must still pay for their crimes. However, some people are deliberately malicious and have evil intentions towards others. If others forgive their evil actions and evil intentions because they think they are 'judging' them, then this allows corruption to prevail.