Mishkat al-Masabih 19 Jihad كتاب الجهاد 194

وَعَنْ نُعَيْمِ بْنِ مَسْعُودٍ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ لِرَجُلَيْنِ جَاءَا مِنْ عِنْدِ مُسَيْلِمَةَ: «أَمَّا وَاللَّهِ لَوْلَا أَنَّ الرُّسُلَ لَا تُقْتَلُ لَضَرَبْتُ أَعْنَاقَكُمَا» . رَوَاهُ أَحْمَدُ وَأَبُو دَاوُد

Nu’aim b. Mas’ud reported God’s Messenger as saying to two men who came from Musailima, “I swear by God that were it not that messengers are not killed, I would cut off your heads.” Ahmad and Abu Dawud transmitted it.