What is the ruling of Islamic law regarding my possession of a sum of money I found on the road, then a man came claiming ownership of it and swore to that effect, and what is the ruling on my giving him the money based on the intervention of another person?

The lost item should not be handed over to its claimant unless he describes it. It is not permissible for the finder to prompt its description when announcing it, for fear that someone who is not its owner might claim it. So, if someone makes a mistake and describes it, or enables someone who is not its owner to see it and claim it, and then its real owner comes and describes it, the finder is obliged to guarantee it.