I heard the Messenger of Allah ﷺ say when they (messengers sent by Musaylimah) read the letter of Musaylimah: What do you believe yourselves? They said: We believe as he believes. He said: I swear by Allah that were it not that messengers are not killed, I would cut off your heads.  

كَانَ مُسَيْلِمَةُ كَتَبَ إِلَى رَسُولِ اللَّهِ ﷺ قَالَ وَقَدْ حَدَّثَنِي مُحَمَّدُ بْنُ إِسْحَاقَ عَنْ شَيْخٍ مِنْ أَشْجَعَ يُقَالُ لَهُ سَعْدُ بْنُ طَارِقٍ عَنْ سَلَمَةَ بْنِ نُعَيْمِ بْنِ مَسْعُودٍ الأَشْجَعِيِّ عَنْ أَبِيهِ نُعَيْمٍ قَالَ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ لَهُمَا حِينَ قَرَآ كِتَابَ مُسَيْلِمَةَ مَا تَقُولاَنِ أَنْتُمَا قَالاَ نَقُولُ كَمَا قَالَ قَالَ أَمَا وَاللَّهِ لَوْلاَ أَنَّ الرُّسُلَ لاَ تُقْتَلُ لَضَرَبْتُ أَعْنَاقَكُمَا  

Harithah ibn Mudarrib said that he came to Abdullah ibn Mas'ud and said (to him): There is no enmity between me and any of the Arabs. I passed a mosque of Banu Hanifah. They (the people) believed in Musaylimah. Abdullah (ibn Mas'ud) sent for them. They were brought, and he asked them to repent, except Ibn an-Nawwahah. He said to him: I heard the Messenger of Allah ﷺ say: Were it not that you were not a messenger, I would behead you. But today you are not a messenger. He then ordered Qarazah ibn Ka'b (to kill him). He beheaded him in the market. Anyone who wants to see Ibn an-Nawwahah slain in the market (he may see him).  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ لَوْلاَ أَنَّكَ رَسُولٌ لَضَرَبْتُ عُنُقَكَ فَأَنْتَ الْيَوْمَ لَسْتَ بِرَسُولٍ فَأَمَرَ قَرَظَةَ بْنَ كَعْبٍ فَضَرَبَ عُنُقَهُ فِي السُّوقِ ثُمَّ قَالَ مَنْ أَرَادَ أَنْ يَنْظُرَ إِلَى ابْنِ النَّوَّاحَةِ قَتِيلاً بِالسُّوقِ