"I heard Mu'awiyah delivering the Khutbah, and he narrated a few Hadiths from the Messenger of Allah [SAW]." He said: "I heard him delivering a Khutbah and he said: 'I heard the Messenger of Allah [SAW] say: Every sin may be forgiven by Allah except a man who kills a believer deliberately, or a man who dies as a disbeliever.'" (Using translation from Nasāʾī 3984)
عَنْ رَسُولِ اللَّهِ ﷺ يَقُولُ قَالَ رَسُولُ اللَّهِ ﷺ «كُلُّ ذَنْبٍ عَسَى اللَّهُ أَنْ يَغْفِرَهُ إِلَّا رَجُلٌ يَمُوتُ كَافِرًا أَوِ الرَّجُلُ يَقْتُلُ مُؤْمِنًا مُتَعَمِّدًا»