Please revert on urgent basis

Dear All

Please suggest me..

We have debited Purchase A/c with 900000/-

Now the supplier has raised a credit note to us for Rs. 50,000/- on account of Billing rate difference.

should i pass the following entry:

Party Dr. 50,000

Purchase A/c Cr 50,000

OR

Party Dr. 50,000

Trade Discount A/c 50,000

Please suggest the correct one

Thanks