Does repentance and seeking forgiveness for eating from ill-gotten wealth become complete by returning the price of the food, or by seeking forgiveness only? And is money taken from a trust considered unlawful in itself or due to how it was acquired?

If the wealth of the person whose food you ate was acquired through usurpation or theft, then you must guarantee what you ate to the owners of this wealth. If you cannot reach them, then give its value in charity on their behalf. However, if his wealth was acquired through forbidden contracts such as usury, then you are not obliged to guarantee what you ate. Some scholars have held the permissibility of eating what he purchased with his ill-gotten gains, because the prohibition relates to his liability and not to what he purchased. It has been narrated from Ibn Masoud that he said: "The enjoyment is yours, and the sin is upon someone else." And whoever takes from trust money without the permission of its owners, it is forbidden for him, and it is not permissible for anyone who knows this to take from it.