Discredit is used with these nouns as the object:
argument, witness

bring, reflect
By telling lies he brought discredit upon the Army.
Your failure reflects no discredit upon you—you did your best.

bring sth into, do sb (both BrE)
She brought the whole system into discredit.
It does us great discredit to treat foreigners so badly.

to sb's discredit
His selfish decision is greatly to his discredit.

discredit to
They were a discredit to their country.