Purchase returns or sales?

I have made credit purchase from my supplier on which he has given me a discount through a credit note.When i return the goods back to him partially can i pass a sales entry - debit the supplier and credit sales a/c? or does it have to be shown as purchase return only? Also should the return entry be nett of the discount that i had received or should i give a separate credit note to the extent of discount received on the goods being returned?