Praise be to Allaah.
We put this question to Shaykh Muhammad ibn Saalih al-‘Uthaymeen, may Allaah preserve him, and he answered as follows:
He should tell him: “I am not going to give you the money, because it was (in payment for) a haraam deed,” and he should give it away in charity. And Allaah knows best.
Sheikh Muhammed Salih Al-Munajjid