You will recognize them by their fruit. Grapes are not gathered from thorns or figs from thistles, are they?

Can a fig tree produce olives, my brothers and sisters, or a vine produce figs? Neither can a salt water spring produce fresh water.

for each tree is known by its own fruit. For figs are not gathered from thorns, nor are grapes picked from brambles.

After noticing in the distance a fig tree with leaves, he went to see if he could find any fruit on it. When he came to it he found nothing but leaves, for it was not the season for figs.