When the Prophet (ﷺ) died and Abu Bakr became his successor and some of the Arabs reverted to
disbelief, `Umar said, "O Abu Bakr! How can you fight these people although 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 said, 'None has the right to be worshipped but Allah', Allah will save his property and
his life from me, unless (he does something for which he receives legal punishment) justly, and his
account will be with Allah?' "Abu Bakr said, "By Allah! I will fight whoever differentiates between
prayers and Zakat as Zakat is the right to be taken from property (according to Allah's Orders). By
Allah! If they refused to pay me even a kid they used to pay to Allah's Messenger (ﷺ), I would fight with
them for withholding it." `Umar said, "By Allah: It was nothing, but I noticed that Allah opened Abu
Bakr's chest towards the decision to fight, therefore I realized that his decision was right." - Hadith Al Bukhari 6925 (islam)
Book 88, Hadith 7
Vol. 9, Book 84, Hadith 59