Let me be clarified a little. If gambling is haram, is the money used for it is also considered haram? Meaning, gambling money will not be accepted by people sharing your belief? If yes, then the Bitcoins used for gambling should also be the same. But I don't think all the Bitcoins in the same wallet that are earned cleanly and properly will also be considered haram. That would not be fair. It is like saying some money in the central banks are used for illegal activities therefore all the money are dirty and are haram.