Sahih Muslim – Zakat and its Importance
Abu Hurairah is reported to have said: “When Allah’s Messenger, upon whom be peace, died and Abu Bakr succeeded him as caliph, some Arabs apostasized, causing Abu Bakr to declare war upon them. ‘Umar said to him: ‘Why must you fight these men?’, especially when there is a ruling of the Prophet, upon whom be peace: ‘I have been called to fight men until they say that none has the right to be worshipped but Allah, and whoever said it has saved his life and property from me except when a right is due in them, and his account will be with Allah.’ Abu Bakr replied: ‘By Allah! I will fight those who differentiate between salah and zakah because zakah is the due on property. By Allah! If they withheld even a young she-goat ( ‘anaq) that they used to pay at the time of Allah’s Messenger, upon whom be peace, I would fight them.’ Then ‘Umar said: ‘By Allah! It was He who gave Abu Bakr the true knowledge to fight, and later I came to know that he was right.’ “