How to account unregistered Purchases and Documentation Proof for Income Tax

Dear chartered,

Hope all are doing good,

Let me explain my doubt,

I have registered under GST and purchased Clothes from unregistered person do i need to pay tax under RCM While filing GSTR-3B??

And they are not providing invoice copy also how can i show my purchases while filing Income Tax Return what will be the impact in invoicing how to record my purchases and how to keep in documentation evidence proof for IT

Please guide me in this 

Thanks in advance