Musnad Ahmad 239
It was narrated that `Ubaidullah bin `Abdullah bin `Utbah said:
When the apostates apostatised at the time of Abu Bakr, ‘Umar said: How can you fight the people, O Abu Bakr, when the Messenger of Allah (ﷺ) said: “I have been commanded to fight the people until they say La ilaha illallah (There is no god but Allah), and whoever says La ilaha illallah, his wealth and his life are protected from me except in cases dictated by Islamic law, and his reckoning will be with Allah`? Abu Bakr said: By Allah, I will most certainly fight those who separate prayer and zakah, for zakah is what is due on wealth. By Allah, if they withhold from me a small she-goat that they used to give to the Messenger of Allah (ﷺ), I will certainly fight them for withholding it. `Umar bin al-Khattab said. By Allah, as soon as I saw that Allah had opened Abu Bakr`s heart to the idea of fighting, I knew that he was right.
حَدَّثَنَا عَبْدُ الرَّزَّاقِ، حَدَّثَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، عَنْ عُبَيْدِ اللَّهِ بْنِ عَبْدِ اللَّهِ بْنِ عُتْبَةَ، قَالَ لَمَّا ارْتَدَّ أَهْلُ الرِّدَّةِ فِي زَمَانِ أَبِي بَكْرٍ رَضِيَ اللَّهُ عَنْهُ قَالَ عُمَرُ كَيْفَ تُقَاتِلُ النَّاسَ يَا أَبَا بَكْرٍ وَقَدْ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أُمِرْتُ أَنْ أُقَاتِلَ النَّاسَ حَتَّى يَقُولُوا لَا إِلَهَ إِلَّا اللَّهُ فَإِذَا قَالُوا لَا إِلَهَ إِلَّا اللَّهُ عَصَمُوا مِنِّي دِمَاءَهُمْ وَأَمْوَالَهُمْ إِلَّا بِحَقِّهَا وَحِسَابُهُمْ عَلَى اللَّهِ فَقَالَ أَبُو بَكْرٍ رَضِيَ اللَّهُ عَنْهُ وَاللَّهِ لَأُقَاتِلَنَّ مَنْ فَرَّقَ بَيْنَ الصَّلَاةِ وَالزَّكَاةِ فَإِنَّ الزَّكَاةَ حَقُّ الْمَالِ وَاللَّهِ لَوْ مَنَعُونِي عَنَاقًا كَانُوا يُؤَدُّونَهَا إِلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لَقَاتَلْتُهُمْ عَلَيْهَا قَالَ عُمَرُ رَضِيَ اللَّهُ عَنْهُ فَوَاللَّهِ مَا هُوَ إِلَّا أَنْ رَأَيْتُ أَنَّ اللَّهَ قَدْ شَرَحَ صَدْرَ أَبِي بَكْرٍ رَضِيَ اللَّهُ عَنْهُ لِلْقِتَالِ فَعَرَفْتُ أَنَّهُ الْحَقُّ‏.‏