Refund to foreign friend

Sir,

Somebody  borrowed Rs.75,00,000/-  (85000 GBP) from foreigner during the year 2006 to 2008 without any agreement or invoice.  It is a interest free money  It was sent to bank account and i have all the transaction details (HSBC Bank).

Now  they want to return that money and  want to know the procedure and documentation/Forms  for remittance.

Is there any auditors certification required.  

Should they collect any lettter from them to refund the money before remittance.

Please advise me.

Regards