'Asim told us, from Abu Wa'il, from Ibn Mu’aiz as-Sa'di who said:

I went out to give water to a horse of mine just before dawn, and I passed by the mosque of Banu Haneefah when they were saying: Musailimah is the messenger of Allah. I went to ‘Abdullah and told him, and he sent the police to bring them. He asked them to repent, and they repented, so he let them go but ‘Abdullah ordered that the neck of Ibnun-Nawwahah be struck. They said: You captured people all for the same reason, then you killed some of them and let some of them go. He said: I heard the Messenger of Allah (ﷺ) say, when this one and Ibn Uthal bin Hajar came, "Do you bear witness that I am the Messenger of Allah?” They said: We bear witness that Musailimah is the messenger of Allah. The Prophet (ﷺ) said: "I believe in Allah and His Messengers. If I were to kill any envoy, I would have killed you." That is why I killed him.