"Fight those who do not believe in Allah, nor in the latter day, nor do they prohibit what Allah and His Apostle have prohibited, nor follow the religion of truth, (which is Islam that abolishes all other religions ) of the people of the Book, (meaning the Jews and the Christians ) until they pay the Jizya (the tax imposed upon them) with willing submission and feel themselves subdued . (with humiliation and submission to the government of Islam.) 9:29."
"When the sacred months are over, slay the idolaters wherever you find them. Arrest them, besiege them, and lie in ambush everywhere for them. If they repent and take to prayer and render the alms levy, allow them to go their way. God is forgiving and merciful." Sura 9:5
"Narrated Abdullah: Allah's Messenger said, "The blood of a Muslim who confesses that none has the right to be worshipped but Allah and that I am His Messenger, cannot be shed except in three cases: in Qisas (equality in punishment) for murder, a married person who commits illegal sexual intercourse and the one who reverts from Islam (Apostate) and leaves the Muslims."
Narrated Ali, "Whenever I tell you a narration from Allah's messenger, by Allah, I would rather fall down from the sky, then ascribe a false statement to him, but if I tell you something between me and you, (not a Hadith), then it was indeed a trick (i.e., I may say things just to cheat my enemy). No doubt I heard Allah's messenger saying, "During the last days there will appear some young foolish people, who will say the best words, but their faith will not go beyond their throats (i.e. they will leave the faith) and will go out from their religion as an arrow goes out of the game. So, wherever you find them, kill them, for whoever kills them shall have reward on the Day of Resurrection."
Not only did Muhammad teach that Muslims are to murder those that have left Islam, "wherever you find them", he further taught that a Muslim who commits this type of murder will be doing God's service and be rewarded!