Matthew 7:16-18

You will fully recognize them by their fruits. Do people pick grapes from thorns, or figs from thistles? Even so, every healthy (sound) tree bears good fruit [worthy of admiration], but the sickly (decaying, worthless) tree bears bad (worthless) fruit. A good (healthy) tree cannot bear bad (worthless) fruit, nor can a bad (diseased) tree bear excellent fruit [worthy of admiration].