Musannaf Ibn Abi Shayba 19:919

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ibn Jurayj, he said: 'Amr ibn Dinar informed me regarding the man who commits disbelief after his belief. He said: I heard 'Ubayd ibn 'Umayr saying: "He is to be killed."