سنن النسائي

It was narrated that Abu Hurairah said: "When the Messenger of Allah (ﷺ) [SAW] died, and Abu Bakr (became Khalifah) after him, and the 'Arabs reverted to Kufr, 'Umar said: 'O Abu Bakr, how can you fight the people when the Messenger of Allah (ﷺ) [SAW] said: I have been commanded to fight the people until they say La ilaha illallah, and whoever says La ilaha illallah, his wealth and his life are safe from me, except for a right that is due, and his reckoning will be with Allah, the Mighty and Sublime?' Abu Bakr said: 'I will fight whoever separates Salah and Zakah, for Zakah is the compulsory right to be taken from wealth. By Allah, if they withhold from me a young goat that they used to give to the Messenger of Allah (ﷺ) [SAW], I will fight them for withholding it.' 'Umar said: 'By Allah, as soon as I saw that Allah has expanded the chest of Abu Bakr to fighting, I knew that it was the truth.'"