What is the ruling on receiving twenty prayer rugs, after having requested and paid for only ten, when the mistake was made by the seller?

If someone finds an excess in what they purchased, they must return it to its owner. If the owner cannot be found, they should give it away as charity on their behalf, or give its value as charity. Then, if they find the owner later, they should give them the choice between ratifying the charity or having its value returned to them.