Ruling on taking more than what was requested due to the worker's error

Question:
The questioner (S. S.) from Abha, whose question we reviewed, has this remaining question: A friend sent a worker to get him lunch and gave him the price for that lunch, which was seven riyals. When the worker brought the lunch, he found it to be more than what was requested, meaning its price was sixteen riyals. He ate it without doing anything about it, assuming that the restaurant owner was the one who made the mistake. Does he have to give the restaurant owner the difference for the extra amount? Or what should this man do?

Answer:
This requires a detailed explanation. If the worker voluntarily gave the extra amount to his friend, then it is on the worker, and there is no harm if he voluntarily gave the extra. However, if he made a mistake and the restaurant owner erred by giving him food worth sixteen riyals while he was mistaken, it is obligatory that the extra amount in which he erred be given back. It is obligatory for the eater to give him the extra. So if there was food worth seven or eight riyals, and the food was worth sixteen, and he was given food known to be worth sixteen, he must complete the payment by giving him the amount of the excess; because his mistake does not make his food lawful for him. But if the restaurant owner, or the worker, was giving it as a gift, then there is no harm. Yes.

The presenter: May Allah reward you, O Shaykh.