Musnad Abu Ya'la al-Mawsili 41:14

Ubayd Allah al-Qawariri narrated to us, Hammad bin Zayd narrated to us, from Muhammad bin Shabib, from Abd al-Malik bin Umayr, from Amr bin Hurayth, from Sa'id bin Zayd, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The truffle is of the manna, and its water is a cure for the eye."