the prophet (sallallahu 'alaihi wa sallam) said, "the example of him (a believer) who recites the qur'an is like that of a citron which tastes good and smells good. and he (a believer) who does not recite the qur'an is like a date which is good in taste but has no smell. and the example of a dissolute wicked person who recites the qur'an is like the raihana (sweet
basil) which smells good but tastes bitter. and the example of a dissolute wicked person who does not recite the qur'an is like the colocynth which tastes bitter and has no smell."

bukhari vol. 6 : no. 538

colocynth - a type of bitter fruit -