From Sahih Muslim (Hadith 5345):
Sa'id b. Zaid b. 'Amr b. Nufail reported Allah's Messenger (ﷺ) 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
Reference: Muslim 5345