Apostasy of the Arab Tribes after the Demise of the Holy Prophet (sa)
When news of the Holy Prophet’s (sa) demise spread, many of the Arab tribes became apostates and refused to pay the Zakat. Hazrat Abu Bakr (ra) decided to fight against them. Urwah relates that Hazrat Abu Bakr (ra) took the Muhajireen and the Ansar along with him and left Medina. When he reached a lake which was situated opposite the mountainous area of Najd, the Bedouins had fled from there along with their families. In actuality they did not completely become apostate, but still claimed to be Muslims and yet refused to pay the Zakat. Thus, it was for this reason that Hazrat Abu Bakr (ra) decided to fight against them and not because they had become apostates.
When these Bedouins fled from there, it was suggested to Hazrat Abu Bakr (ra) that he should return to the women and children left behind in Medina and appoint someone as the commander of the army in his place. Upon the persistent suggestions from others, Hazrat Abu Bakr (ra) appointed Hazrat Khalid (ra) bin Waleed as the commander of the army and said to him, “If they wish to accept Islam and pay the Zakat, (in other words, reaffirm their pledge of allegiance), then if anyone from among them wishes to return, then they can do so.” After this, Hazrat Abu Bakr (ra) returned to Medina.
(Jalauddin Abdur Rahman bin Abi Bakr al-Suyuti, Tarikh al-Khulafa, p. 61, al-Khalifa al-Awwal Abu Bakr Siddiq (ra), Fasl fi ma Waqa‘a fi al-Khilafah)