It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that the Prophet (peace and blessings be upon him) said: "Whoever changes his religion" or he said: "turns back from his religion" "kill him." And he said: "Do not punish with the punishment of Allah," that is, with fire.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11800