Musannaf Ibn Abi Shayba 28:582

Yazid ibn Harun narrated to us, he said: Sufyan ibn Husayn informed us, from al-Zuhri, from Ubayd Allah ibn Abd Allah ibn Utbah, who said: When those who apostatized during the time of Abu Bakr apostatized, Abu Bakr wanted to fight them. Umar said: "Will you fight them when you have heard the Messenger of Allah (peace be upon him) say: 'Whoever testifies that there is no god but Allah and that Muhammad is the Messenger of Allah, his wealth and his life are inviolable except by his right, and his reckoning is with Allah'?" Abu Bakr said: "I will not fight anyone who separates between prayer and zakat. By Allah, I will surely fight whoever separates between them until I unite them." Umar said: "So we fought with him, and it was the right course." When he was victorious over those of them he was victorious over, he said: "Choose between two options from me: either a devastating war or a humiliating submission." They said: "This devastating war, we have known it. But what is the humiliating submission?" He said: "That you testify regarding our killed ones that they are in Paradise, and regarding your killed ones that they are in the Fire." And they did so.