Idiom request for speaking about punishing or scolding somebody before they are proved guilty, just out of prejudgement

Consider the phrase rush to judgment as the action of one who concludes too quickly on the basis of insufficient or misconstrued evidence.

In an article published at stubbornthings.org Jerry Richardson contrasts a rush to judgment with the concept of the Rule of Law expounded by Madison in Federalist No. 51:

Vigilantes often rush to judgment, and get it wrong. Result? Innocent people get killed or otherwise unjustly punished.

I prefer this expression as generally accessible to less cliched than "judging a book by its cover."

Jump to conclusion is just fine.

Don't judge a book by its cover may also convey the idea of an erroneous judgment based just on what something looks like:

• used for saying that you should not form an opinion about someone or something only from their appearance.

(Macmillan Dictionary)