When Allah's Messenger (ﷺ) died and Abu Bakr was elected as a Caliph after him, some of the Arabs
reverted to disbelief, `Umar said to Abu Bakr, "How dare you fight the people while Allah's Messenger (ﷺ)
said, I have been ordered to fight the people till they say 'None has the right to be worshipped but
Allah' And whoever says: None has the right to be worshipped but Allah.' waves his wealth and his
life from me unless he deserves a legal punishment lusty, and his account will be with Allah! Abu
Bakr said, "By Allah, I will fight him who discriminates between Zakat and prayers, for Zakat is the
Compulsory right to be taken from the wealth By Allah, if they refuse to give me even a tying rope
which they use to give to Allah's Messenger (ﷺ), I would fight them for withholding it." `Umar said, 'By
Allah, It was nothing, except I saw that Allah had opened the chest of Abu Bakr to the fight, and I
came to know for certain that was the truth." - Hadith Al Bukhari 7284 (islam)
Book 96, Hadith 16
Vol. 9, Book 92, Hadith 388