Prophet Muhammad (peace be upon him) said:

“The truffle is among the Mann (Allah’s favours) and its water cures the eye”

It was said that among the Manna sent down by Allah to the Children of Israel were several plants that grow in the wild without effort. 
Some scholars consider truffles to be a kind of Manna, although the word Manna in the Quran refers to the sweet dew that descended from the trees.