Sahih al-Bukhari 1399, 1400
Narrated Abu Huraira:
When Allah's Messenger (ﷺ) died and Abu Bakr became the caliph some Arabs renegade (reverted to 
disbelief) (Abu Bakr decided to declare war against them), `Umar, said to Abu Bakr, "How can you 
fight with these people although Allah's Messenger (ﷺ) said, 'I have been ordered (by Allah) to fight the 
people till they say: "None has the right to be worshipped but Allah, and whoever said it then he will 
save his life and property from me except on trespassing the law (rights and conditions for which he 
will be punished justly), and his accounts will be with Allah.' " Abu Bakr said, "By Allah! I will fight 
those who differentiate between the prayer and the Zakat as Zakat is the compulsory right to be taken 
from the property (according to Allah's orders) By Allah! If they refuse to pay me even a she-kid 
which they used to pay at the time of Allah's Messenger (ﷺ) . I would fight with them for withholding it" 
Then `Umar said, "By Allah, it was nothing, but Allah opened Abu Bakr's chest towards the decision 
(to fight) and I came to know that his decision was right."
حَدَّثَنَا أَبُو الْيَمَانِ الْحَكَمُ بْنُ نَافِعٍ، أَخْبَرَنَا شُعَيْبُ بْنُ أَبِي حَمْزَةَ، عَنِ الزُّهْرِيِّ، حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ عَبْدِ اللَّهِ بْنِ عُتْبَةَ بْنِ مَسْعُودٍ، أَنَّ أَبَا هُرَيْرَةَ ـ رضى الله عنه ـ قَالَ لَمَّا تُوُفِّيَ رَسُولُ اللَّهِ صلى الله عليه وسلم وَكَانَ أَبُو بَكْرٍ ـ رضى الله عنه ـ وَكَفَرَ مَنْ كَفَرَ مِنَ الْعَرَبِ فَقَالَ عُمَرُ ـ رضى الله عنه كَيْفَ تُقَاتِلُ النَّاسَ، وَقَدْ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏
"‏ أُمِرْتُ أَنْ أُقَاتِلَ النَّاسَ حَتَّى يَقُولُوا لاَ إِلَهَ إِلاَّ اللَّهُ‏.‏ فَمَنْ قَالَهَا فَقَدْ عَصَمَ مِنِّي مَالَهُ وَنَفْسَهُ إِلاَّ بِحَقِّهِ، وَحِسَابُهُ عَلَى اللَّهِ ‏"‏‏.‏ فَقَالَ وَاللَّهِ لأُقَاتِلَنَّ مَنْ فَرَّقَ بَيْنَ الصَّلاَةِ وَالزَّكَاةِ، فَإِنَّ الزَّكَاةَ حَقُّ الْمَالِ، وَاللَّهِ لَوْ مَنَعُونِي عَنَاقًا كَانُوا يُؤَدُّونَهَا إِلَى رَسُولِ اللَّهِ صلى الله عليه وسلم لَقَاتَلْتُهُمْ عَلَى مَنْعِهَا‏.‏ قَالَ عُمَرُ ـ رضى الله عنه ـ فَوَاللَّهِ مَا هُوَ إِلاَّ أَنْ قَدْ شَرَحَ اللَّهُ صَدْرَ أَبِي بَكْرٍ ـ رضى الله عنه ـ فَعَرَفْتُ أَنَّهُ الْحَقُّ‏.‏