Musnad Ahmad 30:1560

Aswad ibn Amir narrated to us, Aban—meaning Ibn Yazid al-Attar—narrated to us, from Qatadah, from Shahr ibn Hawshab, from Abu Hurairah, that the companions of the Prophet, peace and blessings of Allah be upon him, discussed truffles. They said: "They are the smallpox of the earth, and we do not see that eating them is proper." This reached the Messenger of Allah, peace and blessings of Allah be upon him, so he said: "Truffles are of the Manna, and their water is a cure for the eye. And the Ajwa date is from Paradise, and it is a cure for poison."