Oὐ δύναται δένδρον ἀγαθὸν καρποὺς πονηροὺς ποιεῖν, οὐδὲ δένδρον σαπρὸν καρποὺς καλοὺς ποιεῖν.

A good tree cannot bear bad fruit, nor can a rotten tree bear good fruit.