الأترجة
A fragrant citrus fruit used by the Prophet ﷺ as a simile for the believer who recites Qur'an, and discussed separately by commentators for its digestive properties.
مَثَلُ الْمُؤْمِنِ الَّذِي يَقْرَأُ الْقُرْآنَ كَمَثَلِ الْأُتْرُجَّةِ، رِيحُهَا طَيِّبٌ وَطَعْمُهَا طَيِّبٌ
“The believer who recites the Qur'an is like a citron: its scent is pleasant and its taste is pleasant.” (meaning, not a literal translation)
While this hadith is a spiritual simile rather than a medical instruction, Ibn al-Qayyim discusses citron separately in his medical chapters as beneficial for the heart, digestion, and as a moth-repellent for stored clothing.