He was asked:

A man purchases an item with lawfully acquired money, without knowing whether it was lawfully or unlawfully obtained. If it was in fact unlawfully obtained, does he incur sin?

He answered:

If the buyer believes that the item in the seller’s possession belongs to him and purchases it from him on the basis of outward appearances, he incurs no sin. Even if the seller had actually stolen it, the buyer incurs neither sin nor punishment, whether in this world or the Hereafter. Liability and the obligation to reimburse rest with the person who deceived him and sold it to him.

If the item’s rightful owner subsequently comes forward, his item is returned to him, the buyer is refunded the price he paid, and the wrongdoing seller is punished. Whoever distinguishes between someone who knows and someone who does not know is correct; whoever fails to make this distinction is mistaken. And Allah knows best.