Praise be to Allaah.
You did not explain to us how your friend found this piece
and where he found it?
If this piece of glass has a high value and its owner is
looking for it, and your friend found it in the company or on the street and
the like, then it is lost property and he must look for its owner for a
year. If he does not find him, then he may benefit from it after a year on
the condition that if its owner comes some day, he will give it to him -- if
he still has it -- or he will give him its value if he has sold it.
For more information on the rulings on lost property, please
see the answer to question number
There is nothing wrong with your companion selling this piece
on the basis that it is a piece of glass, but it is not permissible for him
to sell it to one who he thinks most likely will sell it on the basis that
it is a diamond and will deceive and cheat the purchaser, because that is
cooperating in sin and transgression, which Allah has forbidden in the verse
(interpretation of the meaning):
“but do not help one another in sin and transgression”
The scholars of the Standing Committee for Issuing Fatwas
Everything that will be used for haraam purposes or it is
thought most likely that it will be used in that manner, it is haraam to
make it, import it, sell it and distribute it among the Muslims. End quote.
Fataawa al-Lajnah al-Daa’imah, 13/109.