You Must Turn to Allah in Repentance and Seek His Forgiveness
Question :
A woman found a piece of gold in the Sacred City of Makkah, she took it and added it to her gold and sold it all. Later, she regretted this, so what is incumbent upon her, may Allah reward you with goodness?
Answer:
She must give its value to the court along with a description of the gold, for it may be that its owner will come and ask the Committee Responsible for Lost Property about it. If the time passed is considerable, then she should give it in charity on behalf of its owner with the (right) intention. Haply, that will be enough if Allah wills along with her turning in repentance and seeking forgiveness. If it occurred recently, then she should give the sum to the Court and the Court will give it to the Committee.
Source:
Ibn Baz
Fatawa Islamiyah, Vol. 5 Page 30