What is the ruling on someone who intentionally takes extra food, beyond what they need, from a restaurant that operates on an open buffet system, in order to eat it at home, and what is incumbent upon them if their action was unlawful?

What the person did is Islamically forbidden, as it violates the implicit agreement of eating one's fill without taking anything home. Therefore, he must pay the restaurant owner the value of what he took and repent to Allah the Almighty. It is worth noting that the ruling on "open buffet" is debated among scholars due to its包含 uncertainty (gharar).