Musnad Ahmad 27:1438

Ishaq ibn Isa narrated to us, Ibn Lahi'ah narrated to us, from Bukayr, from Nafi', from Ibn Umar, who said: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Whoever dies while not in obedience to Allah, he dies having no argument [to present]. And whoever dies having withdrawn his hand from a pledge of allegiance, his death is a death of misguidance."