Mu’adh bin Jabal (RAA) narrated - concerning a man who embraced Islam and then turned to Judaism (i.e. apostated), ‘I shall not sit down until he is killed. That is the Command of Allah and His Messenger, and he gave an order that he must be killed and so he was.’ Agreed upon. In a version by Abu Dawud, ‘He was given a chance to repent and return to Islam but he refused.’