Musannaf Ibn Abi Shayba 28:225

Shababa narrated to us, he said: Ibn Abi Dhi'b narrated to us, from al-Zuhri, from Ubayd Allah ibn Abd Allah ibn Utbah, he said: There were people from Banu Hanifa who were among those who had been with Musaylima the Liar, spreading his narrations and reciting them. Ibn Mas'ud took them to Uthman, so he wrote to him: "Invite them to Islam. Whoever among them testifies that there is no god but Allah and that Muhammad is the Messenger of Allah, may Allah bless him and grant him peace, and chooses faith over disbelief, then accept that from them and release their way. But if they refuse, then strike their necks." So he sought their repentance; some of them repented, and some refused. He struck the necks of those who refused.