Sahih Muslim Book 23, Hadith Number 5088.

Chapter : Excellence of truffles and their use as a medicine for the eyes.

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.