Received my lent money which the debtor acquired from haram source. Is it halal for me?

Some years ago, I've lent some money to my cousin who was in need. He had trouble paying me back for a long time until last week after I knew he got a lot of money enough to pay me back in full. But yesterday I've been told that he won the money from gambling and exactly he paid me all his debt with that money. Is the money halal for me or is it haram only because I know it's came from haram way ? If it is, then should I give him back the money, or donate it to somewhere, or just throw it all away ?