Musnad Ahmad 30:932

Abu Kamil narrated to us, Hammad narrated to us, Ja'far ibn Abi Wahshiyyah narrated to us, from Shahr ibn Hawshab, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) came out to his companions while they were disputing about this tree which "was uprooted from upon the earth, having no stability" [Ibrahim: 26]. They said: "We think it is the truffle." 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. And the 'ajwah (date) is from Paradise, and it is a cure for poison."