jazaakum Allahu khirun
Praise be to Allaah.
It is not permissible for you to keep it; you must return it to the original owner. This is a trust which is in your hands, and you must return it as soon as possible. Your uncle should ask the person who sold it to him for his money back, because he sold something that was not his to sell. And Allaah knows best.
Sheikh Muhammed Salih Al-Munajjid