It is narrated on the authority of Abu Huraira that when the Messenger of Allah (ﷺ) breathed his last and Abu Bakr was appointed as his successor (Caliph), those amongst the Arabs who wanted to become apostates became apostates. 'Umar b. Khattab said to Abu Bakr
Why would you fight against the people, when the Messenger of Allah declared: I have been directed to fight against people so long as they do not say: There is no god but Allah, and he who professed it was granted full protection of his property and life on my behalf except for a right? His (other) affairs rest with Allah. Upon this Abu Bakr said: By Allah, I would definitely fight against him who severed prayer from Zakat, for it is the obligation upon the rich. By Allah, I would fight against them even to secure the cord (used for hobbling the feet of a camel) which they used to give to the Messenger of Allah (as zakat) but now they have withheld it. Umar b. Khattab remarked: By Allah, I found nothing but the fact that Allah had opened the heart of Abu Bakr for (perceiving the justification of) fighting (against those who refused to pay Zakat) and I fully recognized that the (stand of Abu Bakr) was right.
It is reported on the authority of Abu Huraira that the Messenger of Allah said
I have been commanded to fight against people so long as they do not declare that there is no god but Allah, and he who professed it was guaranteed the protection of his property and life on my behalf except for the right affairs rest with Allah.
It is reported on the authority of Abu Huraira that he heard the Messenger of Allah say
I have been commanded to fight against people, till they testify to the fact that there is no god but Allah, and believe in me (that) I am the messenger (from the Lord) and in all that I have brought. And when they do it, their blood and riches are guaranteed protection on my behalf except where it is justified by law, and their affairs rest with Allah.
It is narrated on the authority of Jabir that the Messenger of Allah said
I have been commanded that I should fight against people till they declare that there is no god but Allah, and when they profess it that there is no god but Allah, their blood and riches are guaranteed protection on my behalf except where it is justified by law, and their affairs rest with Allah, and then he (the Holy Prophet) recited (this verse of the Holy Qur'an):" Thou art not over them a warden" (lxxxviii, 22).
It has been narrated on the authority of Abdullah b. 'Umar that the Messenger of Allah said
I have been commanded to fight against people till they testify that there is no god but Allah, that Muhammad is the messenger of Allah, and they establish prayer, and pay Zakat and if they do it, their blood and property are guaranteed protection on my behalf except when justified by law, and their affairs rest with Allah.
It Is narrated on the authority of Abu Malik
I heard the Messenger of Allah (ﷺ) say: He who professed that there is no god but Allah and made a denial of everything which the people worship beside Allah, his property and blood became inviolable, an their affairs rest with Allah.
Abu Malik narrated on the authority of his father that he heard the Apostle (ﷺ) say
He who held belief in the unity of Allah, and then narrated what has been stated above.