Jesus said that we can judge what people are like by seeing what they do.

Matthew 12:33-37

33 “Think about this: You can know whether a person is good and what that person says is good, in the same way that you can know whether a tree [MET] and the fruit it produces [MET] are good. You can also know whether a person and what that person says is evil in the same way that you can know whether a tree [MET] and its fruit [MET] are blighted. You can know whether a tree is good by seeing its fruit, and similarly people can know the evil character of you Pharisees by listening to your accusations against me. 34 What you teach harms people spiritually like poisonous snakes harm them physically [MET]! You are not able to speak good things because you are evil [RHQ]. Evil people [SYN] like you speak what comes from all that is in their ◄inner beings/hearts►. 35 Good people speak good things. That is like taking good things out of buildings where they are stored. But evil people speak evil things. That is like taking evil things out of buildings where they are stored. 36 I tell you that on the day when God judges [MTY], he will make people recall every useless word they have spoken, and he will judge them accordingly. 37 Based on the words that you have spoken, God will either declare that you are righteous based on the words that you have spoken, or else he will condemn you.”