Madina was surrounded by a ring of tribes whose attitude to Islam was unfavourable if not hostile. The Bani Asad had their concentration at Sumairah, the first stage on the way to Mecca. The Bani Ghatafan had their concentration in the south of Madina. The Banu Tha'lba, the Banu Harrach and the Banu Abas had their stronghold at Abraq. The Banu Dhunayn had their headquarter at Dhul Qissa the first stage on the route from Madina to Nejd.
When Usamah's army left Madina for the Syrian front, the tribes around Madina sent a deputation to wait on Abu Bakr. The tribes were prepared to own Islam, but they refused to pay Zakat. Abu Bakr consulted the companions. Almost all of them advised that as the Muslims were hemmed in by danger from all sides, allegiance of such tribes to Islam should be accepted by foregoing the claim to Zakat, so that there should be no further secession from the fold of Islam.
According to Suyuti's History of the Caliphs, Abu Bakr Ahmad bin Ibrshim al-lsmail, a scholar of the Shaafii school has preserved an account of what happened in the words of Umar himself. The account reads:
"When the Apostle of God died, some of the Arabs fell from the faith and they said 'we will perform the prayers, but we will not pay the poor rate'. I went to Abu Bakr and said 'O Vicegerent of the Apostle of God conciliate the people and be indulgent to them for they are not on a level with brute beasts'. Abu Bakr, replied 'I hoped for your help, and you have come withholding your aid. You were stern in the time of ignorance. Why have you become dissipated and disspirited in Islam? How can I conciliate with them by ignoring the injunctions of Islam? If God and the Holy Prophet had left the matter to the discretion of the community, I could have accepted your advice and allowed concession in the matter of poor rate on the basis of expediency. But where the orders of the Holy Prophet and Allah are conclusive and definite, how can I or you modify such orders, in spite of the gravity of the situation. Alas the Holy Prophet is dead, and divine inspiration is no longer available to us. As the representative of the Holy Prophet it devolves on me to enforce the order passed by the Holy Prophet, and not to modify or amend such order. "Thereupon I realised how correct was Abu Bakr. I congratulated him on his resolve and assured him of my full support".
When the delegation of the tribes waited on Abu Bakr, Abu Bakr explained to the delegates that if they professed Islam, they had to observe all the injunctions of Islam in to. There was no half-way house in Islam, and it was not permissible for them to pick and choose according to their whims in the matter of religion. Islam had either to be accepted or rejected, and there was no room in Islam for any compromise on fundamentals. Zakat being a fundamental injunction of Islam had to be made, and any refusal to pay Zakat implied apostasy. Addressing the delegates, Abu Bakr declared in unequivocal terms:
"Under the circumstances, if with reference to Zakat you withhold even as much as a string to tie a camel, as a Caliph of the Holy Prophet, it will be my duty to fight for it whatever the consequences."
Umar sat by the side of Abu Bakr as the delegates met the Caliph. Thus rebuffed the recalcitrant tribes decided to accept the challenge. As the main Muslim army under Usamah was out of the country, the tribes felt that Madina was vulnerable and would easily fall to any attack. The tribes held a council of war among themselves and decided to attack Madina. One night the tribes marched to Madina and opened the attack.
Abu Bakr and Umar were alive to the gravity of the situation. They took precautionary measures and every able bodied male adult in Madina was called upon to come forward for the defence of the city. With all the forces that could be mustered the Muslims marched to face the invaders. The invaders threw inflated water skins in the path of the Muslim army. That frightened the camels on which the Muslims were riding, and the camels ran towards Madina. The tribes felt jubilant at the retreat of the Muslims.
Abu Bakr and Umar rallied the Muslim forces. In the late hours of the night, the Muslim forces marched out of the city and led a violent attack. The tribal forces were taken unawares and were cut to pieces. Those who survived fled in confusion. Before the day dawned the Muslims had won the victory and the threat to Madina was over.