Musnad Abu Ya'la al-Mawsili 41:21

Zuhayr narrated to us, Jarir ibn Abd al-Hamid narrated to us, from Mutarrif, from al-Hakam, from al-Hasan al-Arani, from Amr ibn Hurayth, from Sa'id ibn Zayd, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The truffle is of the manna which was sent down upon the Children of Israel, and its water is a cure for the eye."