What is the ruling on giving money to a person with an increase when I remember an old debt owed to him that he does not know about, and is it sufficient to give charity to purify the money if I do not remember the owners of the money?

Whoever has someone else's money in their keeping, must return it to its owners, whether it is a trust, a debt due immediately, or a found item whose owner is known. If he forgets the amount of the money, he should strive to clear his conscience and pay the amount he believes is due. Then, the owner of the right should absolve him, or he should pay more than what is due as a precaution.