Abu Hurairah reported,

When the Messenger of Allah ﷺ passed away and Abu Bakr was appointed caliph after him, some of the Arabs reverted to disbelief. Umar bin Khattab said to Abu Bakr, "How can you fight these people when the Messenger of Allah ﷺ said, 'I have been commanded to fight people until they say, There is no god but Allah. Whoever says, There is no god but Allah, has protected from me his wealth and his life, except for what is due upon them, and his reckoning is with Allah'?"Abu Bakr replied, "By Allah, I will fight anyone who separates prayer from zakat, for zakat is the due upon wealth. By Allah, if they withheld from me even a small rope that they used to give to the Messenger of Allah ﷺ, I would fight them for withholding it."Umar bin Khattab said, "By Allah, it was nothing other than that I saw Allah had opened Abu Bakr's heart to fight, so I knew it was the truth."

عن أبي هريرة قال

لما توفي رسول ﷺ، واستخلف أبو بكر بعده، وكفر من كفر من العرب، قال عمر بن الخطاب لأبي بكر: كيف تقاتل الناس وقد قال رسول الله ﷺ: أمرت أن أقاتل الناس حتى يقولوا: لا إله إلا الله فمن قال: لا إله إلا الله فقد عصم منى ماله ونفسه إلا بحقه وحسابه على الله، فقال أبو بكر: والله لأقاتلن من فرق الصلاة والزكاة فإن الزكاة حق المال، والله لو منعوني عقالا كانوا يؤدونه إلى رسول الله ﷺ لقاتلتهم على منعه، فقال عمر بن الخطاب: فوالله ما هو إلا أن رأيت الله عز وجل قد شرح صدر أبي بكر للقتال، فعرفت أنه الحق.