Giving charity on behalf of others

A number of years ago I took one hundred Saudi riyaals from each of a number of colleagues. Later on I travelled to another region and forgot these colleagues, and they forgot me. Now I do not know where they are. What should I do about the money I owe them?
Please tell me, may Allaah reward you.

Praise be to Allaah.

If the case is as you describe in your question, and you have forgotten the person who lent you one hundred Riyaals, then what is prescribed in Islam is that you should give an equivalent amount in charity on their behalf. When you remember any of them, then pay him what you owe him, unless he accepts the fact that you gave charity on his behalf. This will clear you of debt and bring reward to you and to them.