A tree is known by its fruit

People are judged by what they do.

The sources are Matthew, xii, 33 and Luke, vi, 44. Here is the second of these as given in the New English Bible:

There is no such thing as a good tree producing worthless fruit, nor yet a worthless tree producing good fruit. For each tree is known by its own fruit; you do not gather figs from thistles, and you do not pick grapes from brambles. A good man produces good from the store of good within himself; and an evil man from evil within produces evil.