It was narrated from Abu Hurairah that the Prophet (ﷺ) said: “I have been commanded to fight the people until they say La ilaha illallah, and if they say it then their blood and wealth are safe from me, except in cases dictated by sharee'ah, and their reckoning is with Allah.” When some people apostatized, ʼUmar said to Abu Bakr: Will you fight them when you heard the Messenger of Allah is say such and such? Abu Bakr said: By Allah, I will not separate prayer and zakah, and I shall certainly fight anyone who separates them. So we fought them alongside him and we realised that that was the right thing to do.