Musnad Ahmad 30:2338

Hassan ibn Musa narrated to us, Hammad ibn Salamah narrated to us, from Qatadah, and Ja'far ibn Abi Wahshiyyah, and 'Abbad ibn Mansur, from Shahr ibn Hawshab, from Abu Hurairah, that the Messenger of Allah (peace and blessings of Allah be upon him) went out to his companions while they were disputing about the tree which was uprooted from above the earth, having no stability. Some of them said: "I 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."