Sahih Muslim
The Book of Drinks (Kitab Al-Ashriba)
Book Number: 023 / Hadith Number: 5088
Sa'id b. Zaid reported Allah's Messenger (may peace be upon him) as saying: Truffles are 'Manna' which Allah, the Exalted the Majestic, sent to the people of Israil, and its juice is a medicine for the eyes.