Abu Idris al-Khawlani narrates: I heard Sayyiduna Mu'awiyah (may Allah be pleased with him) say: I heard the Messenger of Allah (peace and blessings be upon him) say: "Concerning every sin it is hoped that Allah will forgive it, except the man who dies a disbeliever or the one who kills a believer deliberately."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 16907