Sahih Bukhari
Oneness, Uniqueness of Allah (Tawheed)
Volume: 009 / Book Number: 093 / Hadith Number: 649
Narrated Abu Musa:
The Prophet said, 'The example of a believer who recites the Qur'an is that of a citron (a citrus fruit) which is good in taste and good in smell. And the believer who does not recite the Quran is like a date which has a good taste but no smell. And the example of an impious person who recites the Qur'an is that of Ar-Rihana (an aromatic plant) which smells good but is bitter in taste. And the example of an impious person who does not recite the Quran is that of a colocynth which is bitter in taste and has no smell."