Musannaf Ibn Abi Shayba 33:288

Abu al-Ahwas narrated to us, from Abu Ishaq, from al-Harith, from Ali, who said: The likeness of the one who has combined faith and the Quran is like the citron (utrujjah), which has a pleasant scent and a pleasant taste. And the likeness of the one who has not combined faith and has not combined the Quran is like the colocynth (hanthalah), which has a foul scent and a foul taste.