Payment received from 3rd person other than debtors

Hi Everyone,

I want to know that if I acccept payment from third person on behalf of debtor than what compliance we need to follow? and which additional document we need to maintain?

Eg. Firm Name - A

Debt - B (amount 10000/)

third person - c 

We accept payment from c On the behalf of B.

Thanks in Advance

Shan