"The tree is known by its fruit."

There is a saying , which can be traced back to the Bible :

الشجرة تعرف من ثمارها

“The tree is known by its fruit.”

“Uit de vrucht wordt de boom gekend.”

Other scholars have also said: Hearts are like vessels. When the content of the vessel is pure, then pureness will come out. When the content of the vessel is impure, then impurity will come out. So judge people by their apparant deeds.