Sayyiduna Sa'id bin Zayd bin Amr bin Nufayl (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him): "Truffles are from the manna, and their water is a cure for the eyes."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19568