Hi Vandana!
As per my view, first, you need to collect a request form from the employee titled "Request for Salary in advance."
Then, after approval, on the letterhead of the company, state the employee's name, designation, the amount of advance approved, the repayment process, etc., which has to be specified and signed by the Company and the employee (make two copies).
Additionally, some companies may require certain securities like educational certificates. If you trust, it's well and good.
I believe this should be sufficient.
Regards, Manoj Devda
Accounts and HR Manager