Sahih Muslim
The Book of Drinks (Kitab Al-Ashriba)
Book Number: 023 / Hadith Number: 5086
Sa'id b. Zaid b. 'Amr b. Nufail reported Allah's Messenger (may peace be upon him) as saying: Truffles are a kind of 'Manna' which Allah the Glorious and Exalted, sent down upon the people of Israil, and its juice is a medicine for the eyes.